Opinion of the Advocate-General

I – Introduction

1.The Baltic Sea is surrounded almost entirely by Member States of the European Community. Its condition therefore shows particularly clearly whether European environmental law can prevent the destruction of the marine environment and eliminate damage.

2.The present treaty infringement proceedings concern a particularly serious problem for the Baltic Sea, namely eutrophication, which is an excess of nutrients. The water in the Baltic Sea contains too much nitrogen and phosphorus because these nutrients are discharged in excess into the Baltic Sea from the surrounding land masses. This results in particular in excessive growth of aquatic plants. When these plants die, they extract oxygen from the water. In addition, there may be an increased amount of cyanobacteria (blue-green algae), which produce toxins.

3.The present cases concern nitrogen, which is discharged into the Baltic Sea with urban waste water. Its treatment is regulated by Council Directive 91/271/EEC of 21 May 1991 concerning urban waste water treatment, (2) as amended by Commission Directive 98/15/EC of 27 February 1998 (3) (‘the waste water directive’).

4.On the basis of that directive, the Commission is demanding that Finland and Sweden ensure that all their treatment plants from a certain size reduce the proportion of nitrogen in treated waste water.

5.The Member States concerned contest the Commission’s view, essentially claiming that on account of the conditions in the affected areas of the Baltic Sea, and the Gulf of Bothnia in particular, it is not necessary to reduce nitrogen everywhere in order to prevent eutrophication.

II – Legal framework

A – The waste water directive

6.The waste water directive has applied unreservedly to Sweden and Finland since their accession on 1 January 1995.

7.The basis for the relevant provisions is Article 5(1), (2), (3) and (5) of the waste water directive on the identification of sensitive areas and the treatment of waste water to be carried out in this regard:

‘1. For the purposes of paragraph 2, Member States shall by 31 December 1993 identify sensitive areas according to the criteria laid down in Annex II.

4. ...

8. With regard to more stringent treatment within the meaning of Article 5(2), Annex I.B(3) states:

‘3. discharges from urban waste water treatment plants to those sensitive areas which are subject to eutrophication as identified in Annex II.A(a) shall in addition meet the requirements shown in Table 2 of this Annex.’

‘Requirements for discharges from urban waste water treatment plants to sensitive areas which are subject to eutrophication as identified in Annex II.A(a). One or both parameters may be applied depending on the local situation. The values for concentration or for the percentage of reduction shall apply.’

11. Annex II.A(a) lays down criteria for selecting sensitive areas:

‘A. Sensitive areas

A water body must be identified as a sensitive area if it falls into one of the following groups:

(a) natural freshwater lakes, other freshwater bodies, estuaries and coastal waters which are found to be eutrophic or which in the near future may become eutrophic if protective action is not taken.

The following elements might be taken into account when considering which nutrient should be reduced by further treatment.

(i) lakes and streams reaching lakes/reservoirs/closed bays which are found to have a poor water exchange, whereby accumulation may take place. In these areas, the removal of phosphorus should be included unless it can be demonstrated that the removal will have no effect on the level of eutrophication. Where discharges from large agglomerations are made, the removal of nitrogen may also be considered;

(ii) estuaries, bays and other coastal waters which are found to have a poor water exchange, or which receive large quantities of nutrients. Discharges from small agglomerations are usually of minor importance in those areas, but for large agglomerations, the removal of phosphorus and/or nitrogen should be included unless it can be demonstrated that the removal will have no effect on the level of eutrophication;’

12. Article 2(11) to (13) defines the terms eutrophication, estuary and coastal waters as follows:

‘11. “eutrophication” means the enrichment of water by nutrients, especially compounds of nitrogen and/or phosphorus, causing an accelerated growth of algae and higher forms of plant life to produce an undesirable disturbance to the balance of organisms present in the water and to the quality of the water concerned.

12. “estuary” means the transitional area at the mouth of a river between fresh-water and coastal waters. Member States shall establish the outer (seaward) limits of estuaries for the purposes of this Directive as part of the programme for implementation in accordance with the provisions of Article 17 (1) and (2).

13. “coastal waters” means the waters outside the low-water line or the outer limit of an estuary.’

B – Convention on the Protection of the Marine Environment of the Baltic Sea Area

13.In addition to several Member States and the Russian Federation, the Community is a Contracting Party to the Convention on the Protection of the Marine Environment of the Baltic Sea Area (‘the Baltic Sea Convention’). (5)

14.Article 3 of the Convention contains fundamental principles and obligations, in particular a general obligation to protect and restore the Baltic Sea and a specific definition of the precautionary principle:

‘1. The Contracting Parties shall individually or jointly take all appropriate legislative, administrative or other relevant measures to prevent and eliminate pollution in order to promote the ecological restoration of the Baltic Sea area and the preservation of its ecological balance.

15.With regard to the requirements for treatment plants, the duty to prevent and eliminate pollution from land-based sources laid down in Article 6(1) is particularly relevant:

‘1. The Contracting Parties undertake to prevent and eliminate pollution of the Baltic Sea area from land-based sources by using, inter alia, best environmental practice for all sources and best available technology for point sources. The relevant measures to this end shall be taken by each Contracting Party in the catchment area of the Baltic Sea without prejudice to its sovereignty.

16.Article 19 et seq. lays down rules governing the Baltic Marine Environment Protection Commission, which is based in Helsinki (‘the Helsinki Commission’). All the Contracting Parties are represented in that Commission. In so far as the Community is competent, the Commission represents the Member States.

III – Facts, pre-litigation procedure and forms of order sought

17.In Finland and Sweden agglomerations of more than 10 000 population equivalent must subject their waste water to further treatment for the purposes of Article 5(2) of the waste water directive because both Member States have identified all their waters as sensitive within the meaning of Article 5(1).

18.The Commission takes the view that such further treatment should among other things reduce the proportion of nitrogen in the waste water. Because that is not the case in all the relevant agglomerations of those Member States, it initiated these treaty infringement proceedings and, following invitations to submit observations (letters of formal notice) of 1 July 2002 (Finland) and 23 October 2002 (Sweden), it issued a reasoned opinion to each of the Member States on 1 April 2004.

19.After the two Member States failed to comply with that opinion, the Commission brought an action against Finland (Case C-335/07) on 16 July 2007 and an action against Sweden (Case C-438/07) on 18 September 2007.

20.In Case C-335/07 the Commission claims that the Court should:

– declare that by failing to prescribe more stringent treatment of all waste water entering collecting systems from agglomerations of more than 10 000 population equivalent, the Republic of Finland has failed to fulfil its obligations under Article 5(2), (3) and (5) of Council Directive 91/271/EEC of 21 May 1991 concerning urban waste water treatment;

– order the Republic of Finland to pay the costs.

21.The Republic of Finland contends that the Court should:

– dismiss the action brought by the Commission as unfounded;

– order the Commission to pay the costs.

22.By order of 7 August 2008, the President of the Court of Justice granted leave for the Kingdom of Sweden to intervene in support of the forms of order sought by Finland.

23.In Case C‑438/07 the Commission claims that the Court should:

– declare that the defendant has infringed Article 5(2), (3) and (5) of Council Directive 91/271/EEC of 21 May 1991 concerning urban waste water treatment, as amended by Commission Directive 98/15/EC of 27 February 1998. It has failed to ensure, by 31 December 1998 at the latest, that all discharges from urban waste water treatment plants from agglomerations of more than 10 000 population equivalent released directly into sensitive areas or their catchment areas satisfy the applicable requirements in Annex I to Council Directive 91/271/EEC;

– order the Kingdom of Sweden to pay the costs.

24.The Kingdom of Sweden acknowledges that nitrogen must be removed in 34 treatment plants. In other respects it claims that the Court should:

– dismiss the action.

25.By order of 28 January 2008, the President of the Court of Justice granted leave for the Republic of Finland to intervene in support of the forms of order sought by Sweden.

26.Both Member States and the Commission took part in the joint hearing on 19 February 2009.

27.I will examine these two cases in a joint Opinion as they essentially raise the same questions.

IV – Legal assessment

A – The forms of order sought by the Commission

28.The Commission complains that Finland and Sweden do not subject all waste water from agglomerations of more than 10 000 population equivalent to further treatment. However, the parties are in dispute only as to whether such treatment also requires nitrogen reduction in all cases.

29.The Commission expressly demands that all relevant waste water be subject to nitrogen reduction. On the other hand, it does not object to the decision not to remove nitrogen in certain treatment plants. Rather, the proceedings are based on general considerations: certain areas of the Baltic Sea are sensitive to the discharge of nitrogenous waste water and Sweden and Finland discharge all waste water directly or indirectly into those areas.

30.In so far as the Commission refers to individual treatment plants in the reply, it does so only to illustrate the overall situation. The reasoning is essentially limited to repeating its general arguments. In order to object to individual treatment plants or certain groups of plants, the Commission should have made specific criticisms.

31.If, on the other hand, that submission were intended as an objection to individual plants, the Commission would, as Finland rightly argues, also be modifying the subject-matter of the proceedings compared with the pre-litigation procedure and the application, as individual plants were not under discussion until the reply. That would be inadmissible.

32.The action must therefore be dismissed if this treatment is not necessary only in a few affected treatment plants in each Member State.

33.Consequently, it is irrelevant to the outcome of the action that Sweden acknowledges expressly (6) and Finland at least implicitly (7) that further efforts to remove nitrogen must be made in some treatment plants. Those Member States dispute that this is necessary in many treatment plants.

B – The obligation to reduce nitrogen

34.The basis for the legal examination of the action is Article 5(2) of the waste water directive. Under that provision, the competent authorities must take the necessary measures to ensure that urban waste water entering collecting systems is before discharge into sensitive areas to be subject to more stringent treatment than that described in Article 4 of the directive, by 31 December 1998 at the latest, for all discharges from agglomerations of more than 10 000 population equivalent.

35.Under Annex II.A, the identification of sensitive areas can be based on various criteria, namely eutrophication (a), abstraction of drinking water (b) and prescriptions under other directives (c). There may therefore be sensitive areas for which the discharge of nitrogen and/or phosphorus has no practical relevance. However, both Member States have indisputably declared all their waters to be sensitive from the point of view of eutrophication.

36.The rules to which the more stringent treatment of discharges in such sensitive areas is subject can be seen from a chain of reference: Article 5(3) of the waste water directive refers to Annex I.B. Annex I.B(3) refers in turn to the requirements in Table 2 of that annex. In addition, the Court has already found that those requirements apply subject to the provisions of the second paragraph of Annex II.A(a) to the directive. (8)

37.Table 2 of Annex I contains specific requirements for reducing phosphorus and nitrogen in waste water. According to the heading of that table, however, it depends on the local situation whether nitrogen or phosphorus or both nutrients are reduced. Furthermore the second paragraph of Annex II.A(a) provides that consideration is to be given to which nutrient should be reduced.

38.It follows that nitrogen reduction is not mandatory, but there is some flexibility in the organisation of further treatment. (9) In principle it is to be inferred from the reason for the sensitivity of the area whether nitrogen or phosphorus must be reduced. Under Annex II.A(a), water bodies which are found to be eutrophic or which in the near future may become eutrophic if protective action is not taken are sensitive.

39.The parties are therefore in agreement that nitrogen must be reduced in principle if the discharge of nitrogen contributes to eutrophication or if reducing the discharge is a measure which may prevent future eutrophication.

C – The burden of proof

40.Nevertheless, there is disagreement as to whether the Commission must prove that nitrogen reduction is necessary or whether, conversely, the Member States concerned must show that it is not necessary.

41.The two reports commissioned by the Commission on the implementation of the waste water directive in Finland (10) and Sweden (11) expressly affirm that the Member State concerned must prove that not reducing nitrogen has no effects on the eutrophication of the affected waters. If reasonable doubt exists to suggest that not reducing nitrogen causes damage, treatment is necessary. Accordingly, the Commission argues on several occasions that the Member State in question has not demonstrated certain points. (12)

42.The Court has consistently held, however, that in proceedings for failure to fulfil obligations it is incumbent upon the Commission to prove the allegation that the obligation has not been fulfilled. It is the Commission’s responsibility to place before the Court the information needed to enable the Court to establish that the obligation has not been fulfilled, and in so doing the Commission may not rely on any presumption. (13)

43.Thus, the Commission must in principle show that it is necessary to reduce nitrogen in waste water in order to prevent eutrophication. However, that burden of proof is reduced as a result of the Member States’ obligation to cooperate in good faith and the precautionary principle.

44.First of all, the Member States are required, under Article 10 EC, to support the Commission in ensuring that Community law is applied. (14) It is primarily for the national authorities to conduct the necessary on-the-spot investigations in a spirit of genuine cooperation. (15) Where the Commission has adduced sufficient evidence of certain matters in the territory of the defendant Member State, it is incumbent on the latter to challenge in substance and in detail the information produced and the consequences flowing therefrom. (16)

45.The present case illustrates this cooperation, since the scientific framework for the proceedings is evidently based on research which the two defendant Member States have sponsored themselves and consulted for their own environmental policy. (17)

46.Furthermore, it is enough to prove relevant effects on the environment pursuant to the precautionary principle if, given the available scientific and technical knowledge, the degree of probability of the effect is sufficient. (18) This interpretation of the precautionary principle is consistent with Article 3(2) of the Baltic Sea Convention, under which no conclusive evidence is required of a causal relationship between inputs and their alleged effects. However, the Member States may refute the relevant arguments made by the Commission by means of their own scientific evidence. (19)

47.The Commission states however that, in the case concerning Finland in particular, letters (i) and (ii) of the second paragraph of Annex II.A(a) to the waste water directive lay down specific rules for two special cases of particular sensitivity. These also affect the burden of proof.

48.The first case under letter (i) concerns inland waterways, namely lakes and streams reaching lakes/reservoirs/closed bays which are found to have a poor water exchange, whereby accumulation may take place. In these areas, the removal of phosphorus should be included unless it can be demonstrated that the removal will have no effect on the level of eutrophication. Where discharges from large agglomerations are made, the removal of nitrogen may also be considered.

49.With regard to phosphorus, the refutable presumption is therefore made that its removal is necessary unless the contrary is proven. As Finland argues, the wording of that provision emphasises, as far as the nitrogen reduction at issue in the present case is concerned, only that it is not always necessary. In this respect the general rules on the burden of proof continue to hold.

50.On the other hand, letter (ii) provides that for large agglomerations, the removal of phosphorus and/or nitrogen should be included unless it can be demonstrated that the removal will have no effect on the level of eutrophication. This applies to discharges in estuaries, bays and other coastal waters which are found to have a poor water exchange, or which receive large quantities of nutrients. These rules reverse the burden of proof as regards the need to remove nitrogen.

51.In order to reverse the burden of proof, the Commission must show that the waste water, first of all, comes from large agglomerations and, secondly, is discharged in estuaries, bays or other coastal waters which are found to have a poor water exchange or which receive large quantities of nutrients.

52.The Commission argues that the coastal waters of Sweden and Finland have a poor water exchange because of the irregular coastline and the large number of islands. Large quantities of nutrients are also received.

53.This statement may be true of large parts of the coastal waters. However, the Commission would have to show that all waste water is discharged directly or indirectly into such waters. In order to prove this it is not sufficient to refer to general characteristics of the coastal landscape. As Sweden stresses, it cannot automatically be assumed that there is a poor water exchange in all coastal waters. In all likelihood, at least some waste water is discharged in coastal waters with a high water exchange, so that the nitrogen load is sufficiently diluted out at sea.

54.Because the submission regarding the general characteristics of the coastal waters is not made specific to certain areas, it cannot reverse the burden of proof for specific discharges either.

55.Furthermore, in the view of the Commission, at least the northern part of the Gulf of Bothnia, the Bothnian Bay, as the end of one branch of the Baltic Sea with a poor water exchange with the North Sea and the Atlantic, is a bay within the meaning of letter (ii) of the second paragraph of Annex II.A(a) to the waste water directive.

56.Sweden contends that such a broad application of the term ‘bay’ is incompatible with the meaning of the word. In the view of Finland, the Bothnian Bay, exactly like the southern part of the Gulf of Bothnia, the Bothnian Sea, and the Baltic Proper, is a large marine body which contains bays, estuaries and coastal waters.

57.It is actually somewhat unreasonable to regard the Bothnian Bay, at around 300 km long and up to 200 km wide in places, as a bay. Whilst I consider the notion of bay to be sufficiently broad to cover such large bodies of water, such use does tend to stretch the meaning of the word.

58.The systematic context is more important. The general rule is that it depends on the local situation which nutrients have to be removed by more stringent treatment. Letter (ii) of the second paragraph of Annex II.A(a) to the waste water directive merely specifies particular local conditions which exceptionally permit a rebuttable presumption that it is necessary to remove phosphorus and/or nitrogen. It would be incompatible with these rules laying down exceptions for locations with certain characteristics to cover wholesale large bodies of water in which there may be a large number of areas with quite different local conditions.

59.Furthermore, there are doubts whether the notion of large agglomeration in letter (ii) of the second paragraph of Annex II.A(a) to the waste water directive includes all the contested agglomerations. Since it refers to all agglomerations of more than 10 000 population equivalent, all such agglomerations should be regarded as large in order to presume the need to remove nitrogen for all their discharges. The exceptional nature of that presumption also suggests that such an assumption – put forward by the Commission only in response to a query at the hearing – cannot be made. Moreover, it cannot be inferred from the waste water directive that in principle the value of 10 000 population equivalent designates the threshold for large agglomerations. Rather, the directive has even higher threshold values for other requirements, such as 15 000, (20) 100 000 (21) or 150 000 (22) population equivalent.

60.The Commission cannot therefore rely on the reversal of the burden of proof under letter (ii) of the second paragraph of Annex II.A(a) to the waste water directive in the present proceedings.

D – Evidence of the need to reduce nitrogen

61.The Commission must thus show that the discharge of nitrogen from each Swedish or Finnish agglomeration with a population of more than 10 000 contributes to the eutrophication of a sensitive area or that reducing the discharge of nitrogen is a measure which may prevent the future eutrophication of such an area.

62.Sweden and Finland have identified all their waters as sensitive areas, but the present proceedings concern only the effects on marine areas. All treatment plants in the two Member States drain either directly or indirectly into those areas.

63.The parties are in agreement that the waters off the Swedish coast between the Norwegian border and the town of Norrtälje are sensitive to the discharge of nitrogen. This is also true of the waters off the Finnish south coast. The affected marine areas are the Kattegat and the Danish Straits between Sweden and Denmark, the Baltic Proper, and the Gulf of Finland, between Finland and Estonia. Therefore, direct discharges in those areas must indisputably be subject to nitrogen reduction.

64.On the other hand, it is disputed whether nitrogen reduction is also necessary with regard to all discharges in the Gulf of Bothnia (see below under point 1). The Gulf of Bothnia is the marine area between Finland and Sweden. It consists of the northern part, the Bothnian Bay, and the southern part, the Bothnian Sea.

65.In addition, the parties are in dispute as to whether nitrogen reduction is necessary for all discharges in inland waters which drain into the sea only indirectly (see below under point 2).

66.Lastly, Sweden and Finland claim that a reduction of nitrogen discharges may have harmful environmental effects because excessive growth of cyanobacteria (blue-green algae) would be stimulated (see below under point 3).

67.The discharges in the northern part of the Gulf of Bothnia, the Bothnian Bay, are of central importance to the outcome of the present case. It is common ground between the parties that the discharge of nitrogen in those waters does not give rise to eutrophication. Consequently, on the basis of the characteristics of the Bothnian Bay nitrogen reduction is not necessary under the waste water directive.

68.If all nitrogen discharges in that area also remained there, it would be clear that the Commission could not show that all sufficiently large agglomerations in Sweden and Finland have to reduce the nitrogen content of their waste water. Whilst the land areas draining into the Bothnian Bay are sparsely populated, there are relevant agglomerations in both the Member States concerned which discharge waste water directly or indirectly into the Bothnian Bay. Mention can be made, for example, of the Swedish city of Luleå and the Finnish city of Oulu, which both have much more than 10 000 population equivalent.

69.Nevertheless, the Commission argues that a considerable proportion of the nitrogen discharges in the Bothnian Bay later reach the Bothnian Sea and the Baltic Proper. Before it can be examined whether the Commission has proved this factual submission, it must be considered whether the transfer of nutrients between marine areas is actually relevant to the application of the waste water directive and, if so, how much nitrogen must be transferred in order to give rise to the obligation to reduce nitrogen.

The legal importance of the transfer of nitrogen between different marine areas

70.Sweden disputes the Commission’s claim, first of all, from a legal point of view, arguing that the waste water directive makes no provision for account to be taken of transfers between marine areas. Sweden relies on the wording of Article 5(5) of the waste water directive. Under that provision, there is a need for more stringent treatment of discharges from urban waste water treatment plants which are situated in the relevant catchment areas of sensitive areas and which contribute to the pollution of these areas.

71.In the view of the Swedish Government, the Gulf of Bothnia is not part of the catchment area of other marine areas. By analogy with the definition of river basin in Article 2(13) of Directive 2000/60/EC establishing a framework for Community action in the field of water policy (23) (‘the water framework directive’), it believes that a catchment area is the area of land from which all surface run-off flows through a sequence of streams, rivers and, possibly, lakes into the sea at a single river mouth, estuary or delta. This definition is consistent with established hydrological practice. Marine areas, on the other hand, are not part of the catchment area.

72.However, the Court has previously ruled that a discharge for the purposes of Article 5(2) of the waste water directive exists irrespective of whether the waste water discharges directly or indirectly into a sensitive area. (24) This is in keeping with the high level of protection provided by Community policy on the environment under Article 174(2) EC. (25)

73.These cases concerned on the one hand discharges into rivers which transported nutrients into sensitive areas, (26) and on the other percolation, where the nutrients reached the sensitive marine area through the groundwater. (27) However, there is no clear reason to favour nitrogen discharges which do not reach sensitive waters through inland waters or the groundwater, but through marine areas.

74.The notion of catchment area in Article 5(5) of the waste water directive therefore serves primarily an illustrative function. It cannot be considered to limit treatment obligations. In contrast, the water framework directive attaches a much broader function to that notion, which requires a different interpretation.

75.A discharge of nitrogenous waste water in a nitrogen-sensitive area can therefore exist if the discharged nitrogen reaches the area through another marine area.

The necessary quantity of the transfer

76.However, the present cases show that the possibility of an indirect discharge means that it must be clarified what proportion of the nitrogen discharge must reach sensitive areas in order to establish the obligation to reduce nitrogen.

77.The Commission endeavours to show that significant quantities of nitrogen are transferred between the different parts of the Gulf of Bothnia and from there to the Baltic Proper. However, that overall transfer is not the crucial factor. Rather it is relevant whether the discharge of waste water into the Bothnian Bay increases the nitrogen load in sensitive areas. (28) Eutrophication within the meaning of the waste water directive is characterised by a cause and effect relationship between the discharge and the impairment of the water quality. (29)

78.In this regard Sweden claims, with reference to model calculations, that nitrogen discharges from urban waste water represent only an extremely small proportion of the nitrogen transfer between the Bothnian Bay, the Bothnian Sea and the Baltic Proper. (30) Finland submits calculations which produce somewhat higher figures that are still, however, less than one per cent of the annual nitrogen input in the Baltic Sea.

79.Nevertheless, those calculations do not necessarily militate against an obligation for more stringent treatment of waste water. Any discharge is insignificant where it is sufficiently diluted. Dilution effects can be ruled out only in the case of close proximity to the source of the discharge. If account were taken only of the proportion of a pollution source in relation to the overall pollution, it would not really be possible to infer treatment obligations for individual sources from the pollution of large areas. Thus the discharges from Stockholm or Gdansk would presumably be insignificant for the eutrophication of the Baltic Proper because even those discharges each account for only a small proportion of the overall load. However, the waste water directive requires more stringent waste water treatment for all agglomerations of more than 10 000 population equivalent if they discharge in sensitive areas, irrespective of whether the discharge from that agglomeration represents a large or a small proportion of the pollution load.

80.This is not precluded by the necessary cause and effect relationship between the discharge of nitrogenous urban waste water and the deterioration of water quality either. (31) The Court has stated that urban waste water must contribute significantly to the eutrophication of sensitive waters in order to require identification under the waste water directive. (32) However, this relates to the overall pollution of the sensitive waters by urban waste water and not the significance of individual discharges or certain groups of discharges. If individual discharges represent only a small proportion of the overall load, this does not mean that discharges of this kind are not, taken together, significant to the eutrophication of the sensitive waters. It is undisputed in the present case that the Baltic Proper is sensitive to the discharge of nitrogenous urban waste water.

81.However, not all increases in the nitrogen load of a sensitive area which can be attributed to indirect discharges can give rise to the obligation to remove nitrogen. This would be unreasonable since any discharge of nitrogen in any waters presumably increases the nitrogen load of a sensitive area at least in homeopathic doses.

82.The waste water directive already contains a criterion which can be used for assessing the significance of indirect nitrogen discharges, Table 2 of Annex I does not require, as far as further treatment is concerned, thorough treatment, but – in the case of nitrogen – a reduction of at least 70% to 80%. Therefore, a treatment plant may in principle discharge 30% of the nitrogen load contained in waste water directly into a sensitive area. Indirect discharges may not be subject to more stringent requirements.

83.Indirect discharges into sensitive waters are therefore to be treated as if the non-sensitive waters through which the discharges are transported were part of the waste water treatment process. If the transfer waters reliably retain a sufficiently large proportion of the discharged nitrogen, no further treatment in the treatment plant is necessary.

84.Sweden evidently applies this idea to discharges in non-sensitive inland waters. If a sufficient amount of nitrogen is retained en route to the sensitive coastal waters, the treatment plants do not carry out further treatment.

85. The Commission takes the view that the waste water directive does not permit account to be taken of the natural reduction in the proportion of nitrogen during transportation into sensitive waters. However, that opinion is not supported by the directive. As a result of that reduction, the nitrogen remains in waters which are not sensitive to that substance. However, the nitrogen reduction under Article 5(2) is necessary only if there is a relevant sensitivity.

86. The Commission rightly points out, however, that the quantity of nitrogen naturally transported is not constant, but can be subject to variations. In contrast, it must be assumed that a technical nitrogen reduction process can guarantee fairly reliably certain treatment values. Account must be taken of this higher risk of variations when examining how much nitrogen reaches the sensitive area. As Sweden argues in connection with discharges in inland waters, consideration must be given to a careful investigation of nitrogen transportation, as well as the relevant safety margins. However, the possibility of variations cannot justify making indirect discharges subject to much more stringent requirements than direct discharges.

87. An indirect discharge of nitrogen in nitrogen-sensitive areas therefore gives rise to the obligation to reduce nitrogen only if more than 30% of the nitrogen contained in the waste water reaches the sensitive areas.

Application to discharges in the Gulf of Bothnia

88. The Commission claims that 62% of nitrogen inputs in the Bothnian Bay are transported on into the Bothnian Sea. This proportion, which is disputed by Sweden, suggests that a corresponding proportion of nitrogen inputs is also exported by urban waste water. If the Bothnian Sea as a whole were sensitive to nitrogen, such a transfer would be sufficient to give rise to the obligation to reduce nitrogen for discharges into the Bothnian Bay.

89. According to the reports submitted by the Commission on the implementation of the waste water directive in Finland and Sweden, however, there is no eutrophication problem in open sea areas of the Bothnian Sea. The situation is different in coastal waters with low water exchange and high nutrient loads. It is also assumed that nutrient inflows from the Baltic Proper and the Gulf of Finland on the Finnish coast lead to more frequent algae blooms. (33)

90. Even though, according to those reports, certain coastal waters of the Bothnian Sea are sensitive to nitrogen discharges, those findings do not allow the assumption to be made that this applies to the Bothnian Sea as a whole. It is also unlikely that nitrogen discharges into the Bothnian Bay specifically influence the sensitive areas of the Bothnian Sea. First of all, coastal waters with a poor water exchange are affected. Less water will flow there from the Bothnian Bay. In so far as problems are attributed to nutrient inflows, they are inflows from the south, that is to say from the opposite direction.

92. The Commission also takes the view that sufficient quantities of the nitrogen discharged into the Bothnian Bay reach the Baltic Proper, which is sensitive to nitrogen inputs. However, it does not present any information indicating what proportion of the nitrogen discharges into the Bothnian Bay reach the Baltic Proper.

93. According to the reports submitted by it, around 11% of the inputs in the Gulf of Bothnia as a whole are exported to the Baltic Proper. (34) This transfer rate is much lower than the transfer between the Bothnian Bay and the Bothnian Sea. It is consistent with the finding that the Bothnian Sea is an effective sink for nitrogen. (35)

94. The Swedish Government submits the results of a model calculation which produce an even lower transfer rate. Thereunder, reducing nitrogen in waste water discharges in the Gulf of Bothnia by a total of 817 tonnes reduces the nitrogen transfer into the Baltic Proper by only 56 tonnes. In other words, only around 7% of the nitrogen reduction reaches the nitrogen-sensitive Baltic Proper. It must therefore be presumed that the transfer rate for discharges is not much higher.

95. It is not necessary to examine here which of the calculations is accurate. Both estimates tend to suggest at least that no more than 30% of the discharges into the Bothnian Bay reach the Baltic Proper. In this connection I have not yet taken into account the fact that according to the submissions made by Sweden and Finland, which are undisputed in this regard, 30% of the nitrogen is removed by waste water treatment within the meaning of Article 4 of the waste water directive which must be carried out irrespective of the sensitivity of the discharge areas.

96. The Finnish Government submits figures suggesting a much higher transfer rate. (36) At the hearing, however, it made clear, in response to a query, that it did not call into question the Commission’s figures and that it only submitted gross figures which did not fully represent the transfer. In particular, the quantity of nitrogen retained on transportation is not taken into consideration. Consequently, these figures likewise do not suggest a transfer rate of more than 30%, which it was moreover incumbent on the Commission to show.

97. Thus, the Commission has failed to show that the discharge of nitrogenous urban waste water into the Bothnian Bay reaches sensitive areas of the Baltic Proper in sufficient quantities. Consequently, not all Swedish and Finnish agglomerations of more than 10 000 population equivalent have to subject their waste water to such treatment and, for that reason, both actions must be dismissed. The discharges into the Bothnian Sea are therefore irrelevant.

98. This finding is confirmed by the Helsinki Commission’s Baltic Sea Action Plan. This Plan, which was formulated with Community involvement, requires a reduction of nitrogen inputs in the Baltic Proper, in the Gulf of Finland, in the marine area between Denmark and Sweden (‘Danish Straits’) and in the Kattegat, but the nitrogen discharges in the Bothnian Bay and in the Bothnian Sea do not need to be reduced. (37)

99. I will, however, also examine below the equally disputed questions of discharges in inland waters and the possible excessive growth of cyanobacteria (blue-green algae).

100. The Commission takes the view that Finland, like Sweden, must subject all waste water discharged in inland waters to further nitrogen reduction.

101. As regards discharges in inland waters which reach nitrogen-sensitive areas indirectly, the same must apply as for nitrogen transportation between marine areas: if more than 30% of the nitrogen contained in the waste water reaches the sensitive area, the nitrogen must be reduced.

102. Inland waters eventually drain into coastal waters. In doing so, they transport the nitrogen discharged with urban waste water into the sea. In my opinion, this is essentially sufficient evidence to assume that enough nitrogen reaches the sensitive areas of the Baltic Sea, in particular the Baltic Proper, from discharges into inland waters.

103. However, Finland and Sweden claim, without being challenged, that in the case of simple waste water treatment only 70% of the nitrogen originally contained in the waste water is discharged. Furthermore, Finland and Sweden argue that discharges of nitrogen into inland waters are often reduced naturally before they reach the sea. In lakes in particular, nitrogen is deposited. According to Finland, between 19% and 80% of the nitrogen is reduced in Finnish lakes en route to the sea.

104. In both cases, the Commission objects to generalising the reduction rates nationally. However, that is not the crucial point of these arguments. Both Member States illustrate that in examining individual treatment plants in their own countries the authorising authorities could reach the firm conclusion that a reduction of nitrogen was not necessary.

105. Furthermore, the Commission does not refute the argument made by both Member States that those examinations of the individual case certainly did not apply only general assumptions on nitrogen retention, but that specifically the local situation and nitrogen reduction in the affected waters were taken into consideration. In particular, it does not object to the decisions on individual treatment plants and the methods for calculation of natural nitrogen reduction used in each case.

106. Furthermore, the Commission takes the view that the waste water directive does not permit consideration to be given to the natural reduction of nitrogen. However, there is no clear legal basis for a general rule on this content. Rather, it is correct that according to the definition in Article 2(11) eutrophication requires in particular a disturbance of the natural balance. (38) More stringent treatment is not necessary provided the discharge of nitrogenous waste water does not disturb that balance or is to be expected in accordance with Annex II.A(a).

107. However, the Commission rightly states that the seasonal variations in the natural reduction of nitrogen must be taken into consideration in the specific examination of individual treatment plants. Observance of the threshold value must be continually guaranteed in exactly the same way as in the case of technical nitrogen reduction in a treatment plant. However, this can be examined only with reference to individual plants, which the Commission has not done in the present case.

108. Thus, the Commission has not shown that all treatment plants in Finnish and Swedish agglomerations of more than 10 000 population equivalent which discharge into inland waters must carry out further nitrogen reduction.

109. In addition, I would like to examine briefly one argument in defence presented by Sweden and Finland which is no longer relevant in the present case. The two Member States rely on the risk of excessive growth of cyanobacteria (blue-green algae).

110. If both nitrogen and phosphorus are present in sufficient quantities, plant algae, which are reliant on both nutrients, will clearly grow above all. If, however, there is an excess of phosphorus, this may stimulate the growth of cyanobacteria, as these do not have to extract the necessary nitrogen from the water, but can also use atmospheric nitrogen. An excess of cyanobacteria is undesirable primarily for three reasons:

– they form a slimy mass on the surface of the water;

– they produce toxins;

– the atmospheric nitrogen fixed increases the nitrogen load in the waters.

111. The two Member States consider that the discharge of nitrogenous urban waste water into waters with an excess of phosphorus could contribute to preventing the excessive growth of cyanobacteria. They argue that this risk therefore justifies not carrying out further nitrogen reduction where there is an excess of phosphorus.

112. In this respect it should be borne in mind that nitrogen reduction has to be carried out only where it is necessary. An element of that necessity is certainly also damage caused by nitrogen reduction. This has already been recognised by the Court when it held that in connection with further treatment sufficient account may be taken of demand for nutrients in commercial plankton production in sensitive waters. (39) This statement should not be construed as meaning that eutrophication can be accepted in order to satisfy commercial interests. However, the organisation of the further treatment is in any case open to consideration of the advantages and disadvantages.

113. It may therefore be possible to carry out nitrogen reduction in order to counter the risk of excessive growth of cyanobacteria. However, the burden of proof for this risk, its magnitude and the effectiveness of not reducing nitrogen rests with the Member State which relies on it. Under the waste water directive, nitrogen must normally be reduced if it contributes to the risk of eutrophication.

114. There is, however, no need to decide in the present case whether the two Member States have furnished that proof. (40)

V – Costs

115. Under Article 69(2) of the Rules of Procedure, the unsuccessful party is to be ordered to pay the costs if they have been applied for in the successful party’s pleadings. The Commission has been unsuccessful with both actions, but Sweden has not asked for costs in its pleadings. Therefore the Commission is to pay the costs in Case C‑335/07 and the parties are to bear their own costs in Case C‑438/05.

116. Under Article 69(4) of the Rules of Procedure, the Member States which have intervened in the proceedings are to bear their own costs.

VI – Conclusion

117. I therefore propose that the Court should:

118. In Case C-335/07:

(1) dismiss the action;

(2) order the Commission to pay the costs with the exception of the costs incurred by the Kingdom of Sweden.

119. In Case C-438/07:

(1) dismiss the action;

(2) order the Commission of the European Communities, the Kingdom of Sweden and the Republic of Finland to bear their own costs.

(1) .

(2) – OJ 1991 L 135, p. 40.

(3) – OJ 1998 L 67, p. 29.

(4) – My addition.

(5) – OJ 1994 L 73, p. 20, adopted by the Council Decision of 21 February 1994 on the conclusion, on behalf of the Community, of the Convention on the Protection of the Marine Environment of the Baltic Sea Area (Helsinki Convention as revised in 1992), OJ 1994 L 73, p. 19.

(6) – According to Sweden’s submissions, such treatment must still be established or improved in 34 plants.

(7) – According to Finland’s submissions, treatment of this kind is prescribed, but not yet established, in the case of 16 plants.

(8) – Case C‑280/02 Commission v France [2004] ECR I‑8573, paragraph 104 et seq.

(9) – See also Commission v France (cited in footnote 8, paragraph 102).

(10) – Searle et al. (WRc), Evaluation of Finland’s implementation of Directive 91/271/EEC on Urban Waste Water Treatment, May 2004, Annex 5 to the application in Case C‑335/07, p. 31.

(11) – Hamil et al. (WRc), Evaluation of Sweden’s implementation of Directive 91/271/EEC on Urban Waste Water Treatment, September 2003, Annex 2 to the reply in Case C‑438/07, p. 32.

(12) – Paragraphs 4, 36, 37 and 46 of the application and paragraphs 5 and 7 of the reply in Case C‑335/07; paragraph 30 of the application and paragraph 40 et seq. of the reply in Case C‑438/07.

(13) – See, for example, Case 96/81 Commission v Netherlands [1982] ECR 1791, paragraph 6; Case C‑494/01 Commission v Ireland [2005] ECR I‑3331, paragraph 41; and Case C‑150/07 Commission v Portugal [2009] ECR I‑0000, paragraph 65.

(14) – Commission v Ireland , cited in footnote 13, paragraph 42.

(15) – Commission v Ireland (cited in footnote 13, paragraph 45).

(16) – Commission v Ireland (cited in footnote 13, paragraph 44).

(17) – The judgment in Commission v France (cited in footnote 8) is also clearly based to a large extent on investigations by French authorities.

(18) – Commission v France (cited in footnote 8, paragraph 34).

(19) – See Case C‑235/04 Commission v Spain [2007] ECR I‑5415, paragraph 26 et seq.

(20) – Article 3(1), Article 4(1).

(21) – Annex I, Table 2, Column 2.

(22) – Article 6(1), Article 8(5).

(23) – Directive of the European Parliament and of the Council of 23 October 2000 (OJ 2000 L 327, p. 1).

(24) – Case C‑396/00 Commission v Italy [2002] ECR I‑3949, paragraph 29 et seq.; Case C‑119/02 Commission v Greece , not published in the ECR, paragraph 39 et seq.; and Case C‑293/05 Commission v Italy , not published in the ECR, summary printed in [2006] ECR I‑122*, paragraph 30 et seq. See also the Opinion of Advocate General Stix-Hackl in Case C‑416/02 Commission v Spain [2005] ECR I‑7487, point 133 et seq.

(25) – See judgments cited in footnote 24: Case C‑396/00 Commission v Italy, paragraph 31, Commission v Greece , paragraph 41, and Case C‑293/05 Commission v Italy , paragraph 32.

(26) – See Case C‑396/00 Commission v Italy and Case C‑293/05 Commission v Italy , cited in footnote 24.

(27) – Commission v Greece (cited in footnote 24, paragraph 37).

(28) – See Commission v France (cited in footnote 8, paragraph 77).

(29) – Commission v France (cited in footnote 8, paragraphs 19 and 40).

(30) – 19 tonnes per year between the Bothnian Bay and the Bothnian Sea and 56 tonnes per year between the Bothnian Sea and the Baltic Proper.

(31) – See, in that regard, Commission v France (cited in footnote 8, paragraph 19).

(32) – Commission v France (cited in footnote 8, paragraph 25; see also paragraphs 40, 52, 67, 77 and 87).

(33) – Hamil et al. (cited in footnote 11, p. 18) and Searle et al. (cited in footnote 10, p. 17 et seq.).

(34) – Hamil et al. (cited in footnote 11, p. 25) and Searle et al. (cited in footnote 10, p. 24).

(35) – Hamil et al. (cited in footnote 11, p. 25) and Searle et al. (cited in footnote 10, p. 24).

(36) – See Annex 1 to the rejoinder.

(37) – HELCOM Baltic Sea Action Plan, http://www.helcom.fi/BSAP/ActionPlan/en_GB/ActionPlan/, p. 8.

(38) – See Commission v France (cited in footnote 8, paragraph 20 et seq.).

(39) – Commission v France (cited in footnote 8, paragraph 102).

(40) – Doubts are raised by the article, cited by Sweden, by Vahtera et al., ‘Internal Ecosystem Feedbacks Enhance Nitrogen-fixing Cyanobacteria Blooms and Complicate Management in the Baltic Sea’, Ambio Vol. 36, No. 2–3, p. 186 et seq., http://ambio.allenpress.com/archive/0044-7447/36/2/pdf/i0044-7447-36-2-186.pdf, according to which both nitrogen and phosphorus should be removed.