JUDGMENT OF THE COURT (Third Chamber)

10 December 2009 ( )









Table of contents





I – Legal context

II – Background and pre-litigation procedure

A – Case 1998/2265 (England, Wales and Scotland)

B – Case 2003/2008 (Northern Ireland)

III – The action

A – The first complaint: failure to identify all sensitive areas

1. Preliminary observations

a) The concept of eutrophication

b) The burden of proof

c) The relevant date to be taken into account when considering the evidence

2. The areas at issue

a) The Humber Estuary

i) The first eutrophication criterion: enrichment by nutrients

ii) The second eutrophication criterion: an accelerated growth of algae and higher forms of plant life

iii) The third and fourth eutrophication criteria: undesirable disturbance to the balance of organisms present in the water and to the quality of the water

b) The Wash

i) The first eutrophication criterion: enrichment by nutrients

ii) The second eutrophication criterion: an accelerated growth of algae and higher forms of plant life

iii) The third and fourth eutrophication criteria: undesirable disturbance to the balance of organisms present in the water and to the quality of the water

c) The Deben and Colne Estuaries

i) The first eutrophication criterion: enrichment by nutrients

ii) The second eutrophication criterion: an accelerated growth of algae and higher forms of plant life

– The Deben Estuary

– The Colne Estuary

iii) The third and fourth eutrophication criteria: undesirable disturbance to the balance of organisms present in the water and to the quality of the water

– The Deben Estuary

– The Colne Estuary

d) The Outer Thames Estuary

i) The first and second eutrophication criteria: enrichment by nutrients and an accelerated growth of algae and higher forms of plant life

ii) The third and fourth eutrophication criteria: undesirable disturbance to the balance of organisms present in the water and to the quality of the water

e) Southampton Water

i) The first eutrophication criterion: enrichment by nutrients

ii) The second eutrophication criterion: an accelerated growth of algae and higher forms of plant life

iii) The third and fourth eutrophication criteria: undesirable disturbance to the balance of organisms present in the water and to the quality of the water

f) North East Irish Sea

i) The first eutrophication criterion: enrichment by nutrients

ii) The second eutrophication criterion: an accelerated growth of algae and higher forms of plant life

iii) The third and fourth eutrophication criteria: undesirable disturbance to the balance of organisms present in the water and to the quality of the water

3. Conclusion on the first complaint

B – The second complaint: infringement of the obligations to collect and treat urban waste water

C – Conclusion

Costs

(Failure of a Member State to fulfil obligations – Environment – Directive 91/271/EEC – Urban waste water treatment – Article 3(1) and (2), Article 5(1) to (3) and (5) and Annexes I and II – Initial failure to identify sensitive areas – Concept of ‘eutrophication’ – Criteria – Burden of proof – Relevant date when considering the evidence – Implementation of collection obligations – Implementation of more stringent treatment of discharges into sensitive areas)

In Case C‑390/07,

ACTION under Article 226 EC for failure to fulfil obligations, brought on 17 August 2007,

European Commission, represented by S. Pardo Quintillán, X. Lewis and H. van Vliet, acting as Agents, with an address for service in Luxembourg,

applicant,

v

United Kingdom of Great Britain and Northern Ireland, represented by C. Gibbs and V. Jackson, acting as Agents, D. Anderson QC and S. Ford, barrister,

defendant,

supported by:

Portuguese Republic, represented by L. Inez Fernandes and M.J. Lois, acting as Agents,

intervener,

THE COURT (Third Chamber),

composed of A. Rosas, acting for the President of the Third Chamber, U. Lõhmus and A. Ó Caoimh (Rapporteur), Judges,

Advocate General: P. Mengozzi,

Registrar: C. Strömholm, Administrator,

having regard to the written procedure and further to the hearing on 5 March 2009,

having decided, after hearing the Advocate General, to proceed to judgment without an Opinion,

gives the following

Judgment

1 By its application, the Commission of the European Communities asks the Court to declare that:

– by having failed to identify the Humber Estuary, the Wash, the Deben and Colne Estuaries, the Outer Thames Estuary, Southampton Water and the North East Irish Sea – with the exception of the Solway Firth – as sensitive areas with respect to eutrophication and

– by having failed to subject to more stringent treatment discharges of urban waste water from agglomerations with a population equivalent (p.e.) of more than 10 000 into the Humber Estuary, the Wash, the Deben and Colne Estuaries, the Outer Thames Estuary, Southampton Water and the North East Irish Sea – with the exception of the Solway Firth – and into Lough Neagh and Upper and Lower Lough Erne,

the United Kingdom of Great Britain and Northern Ireland has failed to fulfil its obligations pursuant to Articles 3(1) and (2) and 5(1) to (3) and (5) of, and Annex II to, Council Directive 91/271/EEC of 21 May 1991 concerning urban waste water treatment (OJ 1991 L 135, p. 40).

I – Legal context

2 Article 1 of Directive 91/271 states that the directive concerns the collection, treatment and discharge of urban waste water and the treatment and discharge of waste water from certain industrial sectors, and that the objective of the directive is to protect the environment from the adverse effects of such waste water discharges.

3 Article 2 of Directive 91/271 states:

‘For the purpose of this Directive:

1. “urban waste water” means domestic waste water or the mixture of domestic waste water with industrial waste water and/or run-off rain water;

2. “domestic waste water” means waste water from residential settlements and services which originates predominantly from the human metabolism and from household activities;

3. “industrial waste water” means any waste water which is discharged from premises used for carrying on any trade or industry, other than domestic waste water and run-off rain water;

4. “agglomeration” means an area where the population and/or economic activities are sufficiently concentrated for urban waste water to be collected and conducted to an urban waste water treatment plant or to a final discharge point;

5. “collecting system” means a system of conduits which collects and conducts urban waste water;

6. “1 p.e. (population equivalent)” means the organic biodegradable load having a five-day biochemical oxygen demand (BOD5) of 60 g of oxygen per day;

…

8. “secondary treatment” means treatment of urban waste water by a process generally involving biological treatment with a secondary settlement or other process in which the requirements established in Table 1 of Annex I are respected;

…

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 …;

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

4 Article 3 of Directive 91/271 provides:

‘1. Member States shall ensure that all agglomerations are provided with collecting systems for urban waste water,

– at the latest by 31 December 2000 for those with a [p.e.] of more than 15 000, and

– at the latest by 31 December 2005 for those with a p.e. of between 2 000 and 15 000.

For urban waste water discharging into receiving waters which are considered “sensitive areas” as defined under Article 5, Member States shall ensure that collection systems are provided at the latest by 31 December 1998 for agglomerations of more than 10 000 p.e.

…

2. Collecting systems described in paragraph 1 shall satisfy the requirements of Annex I.A. …’

5 Article 4 of Directive 91/271 provides that Member States are to ensure that urban waste water entering collecting systems shall before discharge be subject to secondary treatment or an equivalent treatment in accordance with the detailed rules set out in that provision.

6 Article 5 of Directive 91/271 states:

‘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.

2. Member States shall ensure that urban waste water entering collecting systems shall before discharge into sensitive areas be subject to more stringent treatment than that described in Article 4, by 31 December 1998 at the latest for all discharges from agglomerations of more than 10 000 p.e.

3. Discharges from urban waste water treatment plants described in paragraph 2 shall satisfy the relevant requirements of Annex I.B. …

…

5. 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 shall be subject to paragraphs 2, 3 and 4.

…

6. Member States shall ensure that the identification of sensitive areas is reviewed at intervals of no more than four years.

7. Member States shall ensure that areas identified as sensitive following review under paragraph 6 shall within seven years meet the above requirements.

…’

7 Annex I to Directive 91/271, headed ‘Requirements for urban waste water’, provides in point A, headed ‘Collecting systems’, that collecting systems are to take into account waste water treatment requirements and that their design, construction and maintenance are to be undertaken in accordance with the best technical knowledge not entailing excessive costs.

8 Annex I.B, headed ‘Discharge from urban waste water treatment plants to receiving waters’, provides in paragraphs 2 and 3 respectively that ‘discharges from urban waste water treatment plants subject to treatment in accordance with Articles 4 and 5 shall meet the requirements shown in Table 1’ and that ‘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 [Annex I]’.

9 Table 1 of Annex I to Directive 91/271 sets, in particular, maximum concentration rates and minimum percentages of reduction for biochemical and chemical oxygen demand and total suspended solids in discharges from urban waste water treatment plants. Table 2 of Annex I, relating to such discharges to areas that are sensitive with respect to eutrophication, sets, in particular, maximum concentration rates and minimum percentages of reduction for total phosphorus and total nitrogen.

10 Annex II to Directive 91/271, headed ‘Criteria for identification of sensitive and less sensitive areas’, provides in point A, which relates to 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:

…

(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.

…’

11 Annex II.B, headed ‘Less sensitive areas’, provides inter alia that, when identifying such areas, the following elements are to be taken into consideration: ‘open bays, estuaries and other coastal waters with a good water exchange and not subject to eutrophication or oxygen depletion or which are considered unlikely to become eutrophic or to develop oxygen depletion due to the discharge of urban waste water’.

II – Background and pre-litigation procedure

A – Case 1998/2265 (England, Wales and Scotland)

12 The United Kingdom published various documents with a view to the identification of sensitive areas for the purposes of Directive 91/271:

– first, in March 1992, a consultation paper entitled Criteria and Procedures for identifying Sensitive Areas and Less Sensitive Areas (Urban Waste Water Treatment Directive) and Polluted Waters (Nitrates Directive) in England and Wales, which indicated the criteria on the basis of which the United Kingdom proposed to identify sensitive areas with respect to eutrophication;

– second, in March 1993, a further consultation paper, entitled Methodology for identifying Sensitive Areas (Urban Waste Water Treatment Directive) and Methodology for designating Vulnerable Zones (Nitrates Directive) in England and Wales, Annex B to which lists the criteria for assessing eutrophication in estuarial and coastal waters;

– third, in January 1997, a report produced by the Comprehensive Studies Task Team, entitled Comprehensive Studies for the purposes of Articles 6 & 8.5 of Directive 91/271 EEC, the Urban Waste Water Treatment Directive (‘the 1997 CSTT report’).

13 In order to check the Member States’ identification of sensitive areas within the meaning of Directive 91/271, the Commission instructed Environmental Resources Management to draw up a set of reports. As regards bodies of water in the United Kingdom, a report entitled Verification of Vulnerable Zones Identified Under the Nitrate Directive and Sensitive Areas Identified Under the Urban Waste Water Treatment Directive, United Kingdom (‘the ERM report’) was published in March 1999.

14 On 4 November 1999 the Commission sent the United Kingdom a letter of formal notice identifying, on the basis of the ERM report, certain areas which, in its view, the United Kingdom should have designated as sensitive areas for the purposes of Directive 91/271, namely the Humber Estuary, the Wash, the Deben and Colne Estuaries, the Outer Thames Estuary, Southampton Water and the North East Irish Sea.

15 The United Kingdom replied by letter of 9 March 2000, drawing attention to the deficiencies that it claimed existed in the ERM report. Additionally, by letters of 6 December 2000 and 7 February 2001, it provided the Commission with peer reviews of the ERM report by Professor D. Nedwell of the University of Essex (Peer Review of ERM Reports for the DETR [Department of the Environment, Transport and the Regions]) and Professor S. Nixon of Rhode Island University, United States (A Review of the Final Report from Environmental Resources Management Ltd to the European Commission).

16 On 19 April 2001 the Commission sent the United Kingdom a reasoned opinion maintaining its complaints concerning the areas identified in the abovementioned letter of formal notice (‘the reasoned opinion of 19 April 2001’), to which the United Kingdom responded on 30 August 2001.

17 The United Kingdom subsequently provided the Commission with further reports assessing the eutrophic status of each of the areas at issue, enclosed, as regards the Humber Estuary, Southampton Water and the Wash, in a letter dated 15 October 2001 and, as regards the Deben and Colne Estuaries, the Outer Thames Estuary and certain areas of the North East Irish Sea (Liverpool Bay and the Solway Firth), in a letter dated 26 November 2001.

18 Finally, by letter of 28 May 2002 the United Kingdom sent the Commission a supplement to the 1993 consultation paper mentioned in the second indent of paragraph 12 of the present judgment, in order to clarify the methodology and approach applied to identify sensitive areas within the meaning of Directive 91/271.

B – Case 2003/2008 (Northern Ireland)

19 In 1994 and 1995 the United Kingdom identified sensitive areas in Northern Ireland for the purposes of Directive 91/271, including Lough Neagh and Upper and Lower Lough Erne.

20 On 11 July 2003 the Commission sent the United Kingdom a letter of formal notice in which it alleged in particular that the United Kingdom had not subjected discharges into those areas from certain agglomerations with a p.e. of more than 10 000 to the more stringent treatment required by Directive 91/271. The United Kingdom responded by letter of 10 September 2003.

21 On 9 July 2004 the Commission sent the United Kingdom a reasoned opinion maintaining its complaints in respect of Lough Neagh and Upper and Lower Lough Erne (‘the reasoned opinion of 9 July 2004’), to which the United Kingdom responded on 9 September 2004.

22 Since the Commission took the view that the situation covered both in that reasoned opinion and in the reasoned opinion of 19 April 2001 remained unsatisfactory, it decided to bring the present action.

23 By order of the President of the Court of 6 February 2008, the Portuguese Republic was granted leave to intervene in the present case in support of the form of order sought by the United Kingdom.

III – The action

A – The first complaint: failure to identify all sensitive areas

24 By its first complaint, the Commission alleges that the United Kingdom has infringed Article 5(1) and Annex II.A(a) of Directive 91/271 by failing to identify the Humber Estuary, the Wash, the Deben and Colne Estuaries, the Outer Thames Estuary, Southampton Water and the North East Irish Sea with the exception of the Solway Firth (‘the areas at issue’) as sensitive areas with respect to eutrophication for the purposes of those provisions.

1. Preliminary observations

a) The concept of eutrophication

25 Since the Commission and the United Kingdom are not in full agreement on the meaning of the term ‘eutrophication’ defined in Article 2(11) of Directive 91/271, it is appropriate, before examining the complaints set out by the Commission in its action, to note the meaning of that term, as explained by the Court in paragraphs 12 to 25 of the judgment in Case C-280/02 Commission v France [2004] ECR I‑8573.

26 As is apparent from paragraphs 13 to 17 of that judgment, the term ‘eutrophication’ defined in Article 2(11) of Directive 91/271 must be interpreted in the light of the directive’s objective, which goes beyond the mere protection of aquatic ecosystems and seeks to conserve man, fauna, flora, soil, water, air and landscapes from any significant adverse effects of the accelerated growth of algae and higher forms of plant life resulting from discharges of urban waste water.

27 As the Court pointed out in paragraph 18 of that judgment, eutrophication is characterised, under Article 2(11) of Directive 91/271, by the fulfilment of four criteria (‘the eutrophication criteria’):

– the enrichment of water by nutrients, especially compounds of nitrogen and phosphorus;

– the accelerated growth of algae and higher forms of plant life;

– an undesirable disturbance to the balance of organisms present in the water;

– an undesirable disturbance to the quality of the water concerned.

28 In addition, for there to be eutrophication within the meaning of Directive 91/271, there must be a relationship of cause and effect between enrichment by nutrients and the accelerated growth of algae and of higher forms of plant life on the one hand and, on the other hand, between that accelerated growth and undesirable disturbance to the balance of organisms present in the water and to the quality of the water (Commission v France, paragraph 19).

29 Finally, it is also to be recalled that, having regard to the aim pursued by the Community legislature, which is to protect the environment from deterioration due to the discharge of urban waste water, the obligation on the Member States under Article 5(1) of Directive 91/271 requires only that they identify the areas where such discharges contribute significantly to eutrophication or the risk of eutrophication (see Commission v France, paragraph 25, and, by analogy, Case C‑293/97 Standley and Others [1999] ECR I‑2603, paragraph 35).

30 In the present case, it must be stated at the outset that, although the ERM report, which predates the judgment in Commission v France by more than five years and upon which the Commission has largely founded the contentions supporting its action, refers to the definition of ‘eutrophication’ in Article 2(11) of Directive 91/271, it does not seek to demonstrate in accordance with a systematic plan that each of the four eutrophication criteria and the causal links between them as set out by the Court in that judgment are established as regards the areas at issue.

31 As the United Kingdom rightly pointed out at the hearing, and as the Commission itself indicated in its application, that report seeks rather to demonstrate that eutrophication of the areas in question can be proved by recourse to a set of environmental factors relating, in particular, to nutrient enrichment, hydrodynamic conditions and the direct and indirect effects of that enrichment. Thus, the authors of the report, referring to the scientific literature, define eutrophication as consisting, essentially, in the increased supply of organic matter in an ecosystem, that is to say, a definition which does not correspond to the eutrophication criteria and the relation between them as set out by the Court in Commission v France.

32 It cannot, however, be inferred from this alone that the ERM report is not capable of demonstrating that the eutrophication criteria under Directive 91/271 are fulfilled with regard to the areas at issue, since the evidential value of the data in that report with regard to those criteria must be specifically assessed at the stage when each of the areas is examined in the light of the content of the report concerning them.

33 As regards more specifically the third eutrophication criterion, the Commission maintains, however, that the proliferation of a single species in itself represents a sufficient disturbance of the ecological balance, since this will often, if not always, entail the reduction of other species. In its submission, so long as the other preconditions are fulfilled, an overall, broadly accepted, measure of accelerated growth of algae and higher forms of plant life, such as that relating to the colouration of water by phytoplankton chlorophyll, can therefore be taken as a demonstration of undesirable disturbance to the balance of organisms present in the water, provided that there is also an undesirable increase in growth, in other words proliferation, compared to background fluctuations.

34 Such a line of argument, which tends to confuse the second eutrophication criterion with the third and fourth criteria, cannot be upheld.

35 Admittedly, the Court held in Commission v France, at paragraph 21, that any proliferation of a particular species of algae or other plant constitutes, as such, a disturbance to the balance of the aquatic ecosystem and, accordingly, to the balance of the organisms present in the water, even when other species remain stable. The Court observed in this connection that, given the competition between plant species for nutrient salts and luminous energy, the proliferation of one or several species, by monopolising the resources necessary for the growth of other algae and aquatic plants, very often if not always entails reductions in other species.

36 However, contrary to what the Commission suggests, the Court also stated, in paragraphs 22 and 23 of that judgment, that the third eutrophication criterion requires that such a disturbance to the balance of organisms present in the water be ‘undesirable’. That undesirability must be considered to be established where there are significant adverse effects on flora or fauna or, given the objective pursued by Directive 91/271, on man, the soil, water, air or landscape. Species change involving loss of ecosystem biodiversity, nuisances due to the proliferation of opportunistic macroalgae and severe outbreaks of toxic or harmful phytoplankton therefore constitute an undesirable disturbance to the balance of organisms present in the water.

37 Similarly, the Court held in paragraph 24 of Commission v France that the fourth eutrophication criterion refers to deterioration of the quality of the water which produces harmful effects for ecosystems and to deterioration of the colour, appearance, taste or odour of the water or any other change which prevents or limits water uses such as tourism, fishing, fish farming, gathering shellfish and shellfish farming, abstraction of drinking water or cooling of industrial installations.

38 It follows that proof of an accelerated growth of algae and higher forms of plant life cannot be considered, as such, to demonstrate undesirable disturbance to the balance of organisms present in the water and to the quality of the water within the meaning of Article 2(11) of Directive 91/271, the undesirability or harmfulness of a proliferation having to be examined not in the context of the second eutrophication criterion, as the Commission suggests, but in that of the third and fourth criteria (see, by analogy, Commission v France, paragraphs 48, 61 and 97).

39 This means, in particular, for the purposes of examining the present action, that, while the chlorophyll concentration level in the water, which enables phytoplankton biomass to be gauged, is capable of demonstrating accelerated growth of algae and higher forms of plant life – a point which the parties accept – it does not, on the other hand, provide any proof of undesirable disturbance to the balance of organisms present in the water or to the quality of the water. As the United Kingdom has argued without contradiction on the Commission’s part, the chlorophyll concentration level in the water provides no information on the number or type of species present or on whether or not they are toxin-producing or harmful. The measurement of that level can therefore be used to detect accelerated growth of algae and higher forms of plant life, but does not enable it to be determined whether that growth is ecologically harmful or results in an undesirable loss of ecosystem biodiversity.

b) The burden of proof

40 The Commission contends that, should the evidence adduced in support of the first complaint not show that the areas at issue were already eutrophic, account needs to be taken of the fact that, under Annex II.A(a) of Directive 91/271, the Member States must also identify areas which ‘in the near future may become eutrophic’ as sensitive areas. The Member States cannot therefore wait until each and every symptom and effect of eutrophication is present before taking action. It follows, for example, that if, in the case of a given body of water, some hydrochemical parameters which may cause eutrophication are present and only one, such as low turbidity, is missing, it may be necessary to classify this body of water as being at risk of becoming eutrophic if protective actions are not taken. The Commission further submits that the United Kingdom authorities have a tendency to recognise the initial warning sign of eutrophication, namely hypernutrification, but do not collect sufficient data – such as data obtained by studying, in particular, the presence of nuisance species, shifts in species, oxygen deficiency or the presence of algal toxins – to disprove the occurrence of eutrophication.

41 The United Kingdom maintains that the Commission places excessive reliance upon presumptions and upon the precautionary principle, in an attempt to make up for its inability to show that certain eutrophication criteria are met or that a causal link between them is present. In particular, the Commission is stated to posit an excessively low threshold of proof as regards waters ‘which in the near future may become eutrophic’ within the meaning of Annex II.A(a) of Directive 91/271. In order for the existence of such a situation to be found, proof is required that the bodies of water concerned are likely to meet the four eutrophication criteria and to display the requisite relationships of cause and effect between those criteria. In the present case, however, the Commission relies on a presumption that, if some symptoms are present, then there is already a likelihood that an area will become eutrophic. The United Kingdom adds that the Commission seeks in a number of respects to shift the burden of proof onto the United Kingdom by alleging a failure on its part to assess the areas at issue, without providing any evidence at all of an undesirable disturbance to the balance of organisms present in the water.

42 It is to be noted that, under Article 5(1) of Directive 91/271, the Member States were to identify by 31 December 1993 areas sensitive with respect to eutrophication in accordance with the criteria laid down in Annex II to that directive, in order to ensure by 31 December 1998 in respect of all discharges from agglomerations of more than 10 000 p.e., in accordance with Article 5(2), that, before discharge into sensitive areas, urban waste water entering collecting systems was subject to more stringent treatment. That obligation to identify sensitive areas entailed collection by the Member States of the data needed for those purposes (see, by analogy, Case C‑221/03 Commission v Belgium [2005] ECR I‑8307, paragraph 79).

43 However, in proceedings under Article 226 EC for failure to fulfil obligations it is for the Commission to prove the allegation that the obligation has not been fulfilled. It is therefore 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 presumptions (see, inter alia, Case C-494/01 Commission v Ireland [2005] ECR I-3331, paragraph 41 and the case-law cited; the judgment of 7 May 2009 in Case C‑530/07 Commission v Portugal, paragraph 32; and the judgment of 6 October 2009 in Case C-335/07 Commission v Finland, not yet published in the ECR, paragraph 46).

44 The Member States are nevertheless required, under Article 10 EC, to facilitate the achievement of the Commission’s tasks, which consist inter alia, pursuant to Article 211 EC, in ensuring that the provisions of the EC Treaty and the measures taken by the institutions pursuant thereto are applied. In particular, account should be taken of the fact that, where it is a question of checking that the national provisions intended to ensure effective implementation of a directive are applied correctly in practice, the Commission, which does not have investigative powers of its own in the matter, is largely reliant on the information provided by any complainants and by the Member State concerned (see, inter alia, Commission v Ireland, paragraphs 42 and 43 and the case-law cited).

45 It follows in particular that, 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 (see Commission v Ireland, paragraph 44 and the case-law cited).

46 Consequently, in the present case, even though the Member States were required to gather the data needed in order to determine the bodies of water that had to be identified as sensitive to eutrophication under Article 5(1) of Directive 91/271, read in conjunction with Annex II thereto, the Commission has the task of adducing in support of the present action for failure to fulfil obligations at least a certain amount of evidence, in respect of each of the areas at issue, first, of fulfilment of the four eutrophication criteria set out in paragraph 27 of the present judgment, in particular as regards the significant adverse environmental effects covered by the last two criteria, and second, of the existence of the relationships of cause and effect referred to in paragraph 28 of the present judgment (see, to this effect, Case C-508/03 Commission v UnitedKingdom [2006] ECR I‑3969, paragraph 78).

47 The same obligation also applies with regard to bodies of water which ‘in the near future may become eutrophic’ within the meaning of Annex II.A(a) of Directive 91/271, the Commission being able at most, in such a case, to demonstrate that, given the available scientific and technical knowledge, the degree of probability of fulfilment of the four eutrophication criteria and of the existence of those relationships of cause and effect is sufficient to require the adoption of the environmental protection measures provided for by that directive (see, by analogy, Commission v France, paragraph 34). Such a requirement of probability falls fully within the scheme and system of the directive since Annex II.B suggests identification of an area as ‘less sensitive’ to eutrophication where the area is ‘unlikely’ to become eutrophic.

48 Therefore, the Commission is certainly right in contending that, in order for a body of water to be identified as a sensitive area with respect to eutrophication for the purposes of Directive 91/271, it is not required to produce evidence showing that all the hydrochemical parameters which may cause such eutrophication, for example regarding temperature or turbidity, are present or to provide irrefutable evidence that each of the eutrophication criteria is fulfilled, and especially that all the adverse effects of an accelerated growth of algae and higher forms of plant life have actually occurred, in particular those which are perceptible at the very end of the eutrophication process, such as shifts in species composition and mortality of benthos and fish. However, the Commission cannot avoid proving, on the basis of specific and coherent evidence, that it is probable that, in the body of water, such accelerated growth caused by nutrient enrichment will, in the near future, produce undesirable disturbance to the balance of organisms present in the water and to the quality of the water. Proof of such probable adverse effects on the environment is therefore in any event required.

49 The question whether, in the case of the water bodies of each of the areas at issue, the Commission does demonstrate to the requisite legal standard, having regard to those criteria, that they were eutrophic or could in the near future become so must, however, be examined in the context of analysis of the arguments it puts forward concerning each of those areas, in the light of the specific evidence and the matters adduced by each party.

c) The relevant date to be taken into account when considering the evidence

50 According to settled case-law, the question whether a Member State has failed to fulfil its obligations must be determined by reference to the situation prevailing in that Member State at the end of the period laid down in the reasoned opinion and the Court cannot take account of any subsequent changes (see, inter alia, Case C‑23/05 Commission v Luxembourg [2005] ECR I-9535, paragraph 9; Case C‑32/05 Commission v Luxembourg [2006] ECR I-11323, paragraph 22; and the judgment of 11 September 2008 in Case C-316/06 Commission v Ireland, paragraph 20).

51 In the present case, it is common ground that, on the date when the period within which the United Kingdom had to act upon the reasoned opinion of 19 April 2001 expired, none of the areas at issue had been identified by it as an area sensitive to eutrophication.

52 Also, under Article 5(1) of Directive 91/271, read in conjunction with Annex II.A(a), the Member States were obliged to identify sensitive areas with respect to eutrophication by 31 December 1993 at the latest.

53 It is accordingly necessary to determine the relevant date to be taken into account for the purposes of examining, in the present action, the evidence adduced by the Commission to show that the eutrophication criteria are established as regards the areas at issue.

54 The United Kingdom observes in this regard that in its application initiating the proceedings the Commission does not allege a breach of Article 5(6) of Directive 91/271, which requires Member States to review the identification of sensitive areas at intervals of no more than four years. In its submission, it follows that the application concerns the alleged failure to identify the areas at issue as sensitive areas as at 31 December 1993, and not at some other time after that date.

55 The Commission states that the starting point of the present case is the absence of such identification of the areas at issue as at 31 December 1993, although there was at that time sufficient evidence to warrant their identification and it was not necessary to await a review under Article 5(6) of Directive 91/271 in order to identify them, but the Commission none the less submits that, should it show that their identification should have occurred at a later stage, the Court should so declare.

56 It is to be observed that it is clear from the wording of the application initiating the proceedings that, as the Commission expressly confirmed in its reply, the present action concerns only an initial failure to identify the areas at issue as sensitive areas with respect to eutrophication as at 31 December 1993, in accordance with Article 5(1) of Directive 91/271, to the exclusion, in contrast to the reasoned opinion of 19 April 2001, of a failure to review the identification of such sensitive areas at intervals of no more than four years as required under Article 5(6), a provision which is indeed not mentioned in the application.

57 When asked about this issue at the hearing, the Commission confirmed that the action was intended to obtain a declaration that the areas at issue should have been identified by the United Kingdom as sensitive areas back in 1993.

58 It follows that the material submitted by way of evidence by the Commission, which has the burden of proving the alleged failure to fulfil obligations, and that adduced by the United Kingdom in rebuttal can have probative value in the context of examination of the present action only if it concerns the state of the areas at issue in light of the eutrophication criteria as at 31 December 1993, which is in principle true of the scientific studies produced by the parties that were drawn up during a period close to that date, whether shortly before or shortly after it.

59 On the other hand, the other scientific studies produced by the parties, the publication date of which shows that they were drawn up at a time far from the period around 31 December 1993, in particular after expiry of the period within which the reasoned opinion of 19 April 2001 had to be acted upon, or even after 17 August 2007, the date upon which the present action was brought, are not in principle capable of having such probative value, save where the evidence which they contain relates to that period and the results which they provide could have been reached from the scientific and technical knowledge of that period.

60 In this connection, account should also be taken of the fact that, in accordance with Annex II.A(a) of Directive 91/271, sensitive areas had to be identified as such by the Member States as at 31 December 1993 if the areas were found to be eutrophic as at that date or they could ‘in the near future’ become eutrophic if protective action was not taken.

61 As the United Kingdom has rightly submitted, and as the Commission indeed accepted at the hearing, since the Member States are obliged, under Article 5(6) of Directive 91/271, to review the identification of sensitive areas at intervals of no more than four years, the words ‘in the near future’ within the meaning of Annex II.A(a) must be understood as referring to a period of roughly four years.

62 First, such a period falls fully within the scheme and logic of the review at regular intervals that is provided for by that directive, enabling account to be taken, including at the time of the initial identification of areas as sensitive with respect to eutrophication as at 31 December 1993, of subsequent changes that may precede the carrying out of a fresh appraisal under Article 5(6) of the directive. Second, that period is sufficiently short to permit, in accordance with what has been held in paragraph 47 of the present judgment, determination with a sufficient degree of probability in particular as to whether, on the basis of the scientific and technical knowledge available as at 31 December 1993, the adoption of the environmental protection measures provided for by the directive was required as regards areas which on that date did not fulfil all the eutrophication criteria.

63 Consequently, in so far as the evidence adduced by the parties concerns a period subsequent to the period around 31 December 1993, it can prove relevant in the context of the present action only if it concerns the situation in the areas at issue during a period up until the end of 1997 (‘the relevant period’). It follows, in particular, that when such evidence is produced by the Commission, it can be sufficient to demonstrate a posteriori, in light of the date on which the present action was brought, that, as at 31 December 1993, those areas were liable to become eutrophic in the near future, so that, if that evidence proves to be sufficient, it is then for the United Kingdom, in accordance with the case-law recalled in paragraph 45 of the present judgment, to rebut its relevance in that regard by challenging it in substance and in detail.

64 It is by reference to these preliminary considerations that the merits of the present action as regards each of the areas at issue falls to be examined.

2. The areas at issue

65 A preliminary point to note is that the Commission and the United Kingdom rely upon certain reports relating to the procedures under the Convention for the Protection of the Marine Environment of the North-East Atlantic of 22 September 1992 (‘the OSPAR Convention’), which has been signed and ratified by, amongst others, the United Kingdom and which entered into force on 25 March 1999. Those reports refer to the identification, between 2000 and 2007, of a series of English coastal waters as ‘Problem Areas’ in respect of eutrophication and to their subsequent declassification. However, without its being necessary to determine whether those areas cover the areas at issue, the parties cannot, in accordance with what has been stated in paragraph 63 of the present judgment, infer from those circumstances any evidence to support their arguments in the context of the first complaint.

66 It should therefore be examined whether the other evidence submitted by the Commission is capable of proving this complaint as regards each of the areas at issue.

a) The Humber Estuary

i) The first eutrophication criterion: enrichment by nutrients

67 While the United Kingdom submits that enrichment of the Humber Estuary by nutrients has decreased significantly in recent years, it does not dispute that during the relevant period there was such enrichment, as indicated by the data in the ERM report adduced by the Commission.

68 The first eutrophication criterion is therefore proven as regards the Humber Estuary.

69 Accordingly, it remains to be examined whether the Commission has proved to the requisite legal standard that the three other eutrophication criteria are fulfilled as regards the Humber Estuary.

ii) The second eutrophication criterion: an accelerated growth of algae and higher forms of plant life

70 The Commission contends that the enrichment of the Humber Estuary by nutrients has resulted in accelerated growth of algae and higher forms of plant life in that estuary. It submits that the Humber Estuary gives rise in this regard to two distinct issues, namely, first, an abundance of phytoplankton in the water and, second, strong intertidal plant growth due to green macroalgae and benthic diatoms on the substrate.

71 First, as regards phytoplankton, the Commission submits that, according to satellite imagery carried out in 1996, the existence of accelerated growth of algae and higher forms of plant life is revealed by phytoplankton chlorophyll present in the sea itself. Indeed, exceptionally high chlorophyll concentration levels have been recorded in the Humber coastal water area. The Commission adds that the United Kingdom did not carry out any systematic monitoring before 2000. It cannot therefore be assumed that all the phytoplankton present were freshwater species. Nor is it correct that phytoplankton growth in the Humber is necessarily low because of high turbidity of the water. The report drawn up by Professor Nedwell at the United Kingdom’s request, referred to in paragraph 15 of the present judgment, mentions moreover that phytoplankton production is considerable in the Humber plume.

72 As to those submissions, it is to be noted that the only concrete evidence adduced by the Commission in support of its contentions concerning the presence of phytoplankton in the Humber Estuary consists in measurement of the chlorophyll concentration level in the water, either by analysing water samples or by assessing remotely the green hue of the water due to the presence of chlorophyll.

73 However, the data supplied by the Commission concerning chlorophyll concentration levels essentially relate to the years 1998 to 2000. Such data, which do not concern the relevant period, cannot therefore demonstrate that the Humber Estuary was eutrophic, or in the near future could become so, as at 31 December 1993.

74 Relying on data provided by the United Kingdom within the framework of OSPAR (Malcolm, S., et al., First Application of the OSPAR Comprehensive Procedure to waters around England and Wales, 2002), the Commission adds, however, that chlorophyll concentrations above 10 µg/l were recorded every year from 1991 to 2000, a period which includes the relevant period. It states that this chlorophyll level is the threshold to be taken into account for the purpose of examining the second eutrophication criterion, relating to proof of accelerated growth of algae and higher forms of plant life.

75 It is therefore appropriate, at the outset, to consider the relevance, which the United Kingdom contests, of that 10 µg/l threshold for demonstrating the existence of such accelerated growth.

76 According to the United Kingdom, the threshold in question, which appears both in the March 1993 consultation paper concerning estuaries and coastal waters and in the 1997 CSTT report concerning coastal waters with a view to defining ‘less sensitive areas’, must be used with some flexibility. Since estuaries are areas of gradation and transition between freshwaters and more saline coastal waters, a graduated threshold according to the salinity of the relevant measuring point should be adopted. Thus, an upper threshold of 100 µg/l is stated to be appropriate for running freshwaters, while an average value, of 25 µg/l, is relevant to the freshwater limit of estuaries, with the limit values then decreasing as the salinity of the water increases, reaching the threshold of 10 µg/l in coastal waters.

77 It must be noted that the Commission does not genuinely contest this methodology. It expressly concedes that, the more saline the water is, the less phytoplankton is acceptable. Moreover, the Commission acknowledged in its application that the taking into account of an absolute threshold of 10 µg/l cannot be a stand-alone method of assessing whether there is accelerated growth of algae and higher forms of plant life, so that that threshold is purely indicative. Furthermore, it is apparent from the Commission’s reply that it shares the view expressed in the 1997 CSTT report, adduced by the United Kingdom in support of its line of argument, that in the case of coastal waters a problem of eutrophication can be revealed only if that threshold is regularly exceeded during the summer. When questioned in this regard at the hearing, the Commission accepted that some flexibility may be adopted regarding use of the 10 µg/l threshold.

78 In those circumstances, it must be held that, as regards the chlorophyll concentration level, only the fact that the 10 µg/l threshold is regularly exceeded, in particular during the summer and in the coastal waters of the estuary, is capable of demonstrating the existence of accelerated growth of algae and higher forms of plant life, and it must be corroborated by other evidence. By contrast, the fact that that threshold is exceeded sporadically, especially if that occurs in the non-coastal waters of the estuary, cannot, as such, be indicative of such accelerated growth.

79 In the present case, the concentration levels relied upon by the Commission all concern the maximum levels achieved in spring during the relevant period, while, according to the same data, the average chlorophyll concentration rate never exceeded the 10 µg/l threshold.

80 The United Kingdom has stated, first of all, that those instances of the threshold being exceeded have been small in number. While acknowledging that it did not systematically record chlorophyll concentration levels before 2000, it relies in this regard on the results of the analysis of 250 samples taken by the Environment Agency between 1992 and 2000, mentioned in its report on the Humber Estuary in response to the reasoned opinion of 19 April 2001 (Urban Waste Water Treatment Directive: Assessment of the Eutrophic Status of the Humber Estuary; ‘the United Kingdom report on the Humber Estuary’).

81 The United Kingdom has secondly explained, on the basis of a study which is more recent (Humber Habitats Directive Review of Consents Report: Nutrient Enrichment, Environment Agency, 2007), but which relates inter alia to the years 1995 to 1997, that the average chlorophyll concentration levels in the Humber Estuary exceeded 10 µg/l during that period only at the single monitoring point at the saline limit, indicating that the chlorophyll observed in that estuary may have been imported from freshwaters.

82 While the Commission has sought to call into question, at least in part, the methodology applied within the framework of the latter study, it has not, on the other hand, contested the sporadic nature of instances where the 10 µg/l threshold is exceeded, an infrequency which is, moreover, borne out by the Modus Vivendi report (Review of UK Implementation of UWWTD [the Urban Waste Water Treatment Directive] for Six Estuarine or Coastal Sites, Final Report, undated; ‘the MV report’), which has been adduced by the Commission and which contains inter alia an examination of the data submitted by the United Kingdom in response to the reasoned opinion of 19 April 2001. It is indicated in that report that the level of chlorophyll in the Humber Estuary ‘is generally low’.

83 Nor has the Commission adduced any evidence capable of rebutting the contention that the high chlorophyll concentration levels observed in the Humber Estuary may result from phytoplankton imported from freshwaters, so that the 10 µg/l threshold would not be exceeded in the coastal waters of that estuary.

84 The data relating to the chlorophyll concentration levels recorded in the Humber plume cannot be used by the Commission in support of the present complaint, since it is not in dispute that this region is located outside the estuary itself and therefore outside the area at issue defined by the Commission in its application.

85 It follows that the Commission has not demonstrated to the requisite legal standard that the concentration of phytoplankton chlorophyll revealed during the relevant period that there was accelerated growth of algae and higher forms of plant life in the Humber Estuary.

86 Second, as regards intertidal plant growth, the Commission states that remote sensing in the form of CASI (Compact Aerial Spectrographic Image) imaging, as carried out in the intertidal areas of the Humber Estuary on 19 August 1996 by the Environment Agency, is intended to indicate nuisance macroalgae growth, by species such as Ulva and Enteromorpha. According to the Commission, the images recorded on that occasion reveal extensive coverage by dense algae in the Humber Estuary, which is indicative of extensive algal growth.

87 As to those submissions, contrary to what the United Kingdom asserts, that capture of images by remote sensing cannot, as such, be regarded as unreliable, the United Kingdom itself indeed having recourse to such images to support certain of its arguments concerning other areas at issue, and it therefore constitutes a means capable of revealing the existence of accelerated growth of algae and higher forms of plant life.

88 However, the Commission relies, here, on a single capture of images carried out nearly three years after the date on which the United Kingdom was to identify sensitive areas with respect to eutrophication as referred to in Directive 91/271, namely 31 December 1993.

89 An isolated capture of images of that kind cannot alone reveal the existence of accelerated growth of algae and higher forms of plant life in the Humber Estuary such as to demonstrate, even a posteriori, that that estuary could have become eutrophic in the near future after that date.

90 That is all the more the case because the MV report, adduced by the Commission in support of its action, itself draws the conclusion that ‘the UK authorities are probably correct to consider that green algae do not occur extensively throughout the Humber Estuary’.

91 It should, moreover, be noted that the Commission did not contest, either in its reply or at the hearing, the explanations provided in the United Kingdom report on the Humber Estuary, which is mentioned in paragraph 80 of the present judgment, to the effect that it follows from a survey carried out in 1996, confirmed by subsequent surveys, that the algae allegedly identified by the images recorded during the remote sensing carried out on 19 August 1996 by the Environment Agency in the form of CASI imaging are, in actual fact, benthic diatoms whose presence on the surface of the mudflats constitutes a natural element of the estuarine ecosystem, which feeds its large bird population.

92 Accordingly, it must be held that those images, in themselves, cannot demonstrate the existence of accelerated growth of algae and higher forms of plant life in the Humber Estuary during the relevant period.

93 The Commission nevertheless maintains that those images are confirmed by the data relating to chlorophyll concentration levels that were provided in the United Kingdom report on the Humber Estuary and following a meeting with the United Kingdom which took place in October 2005. In its submission, those data do reveal chlorophyll concentration levels above the 10 µg/l threshold.

94 It must, however, be stated at the outset that the data provided at the time of that meeting relate to 2002 to 2004, that is to say a period that is not relevant in the present action.

95 As to the data provided in the United Kingdom report on the Humber Estuary, the Commission relies on only two measurements of the chlorophyll concentration level exceeding the alleged 10 µg/l threshold, recorded in mid-1996. As is apparent from paragraph 77 of the present judgment, the Commission has itself acknowledged that that chlorophyll concentration level of 10 µg/l cannot be prescribed as an absolute threshold the exceeding of which is in itself sufficient to establish accelerated growth of algae and higher forms of plant life in a body of water and that a problem of eutrophication can be revealed only if that level is regularly exceeded during the summer.

96 It follows that the Commission has likewise not demonstrated to the requisite legal standard that there was strong intertidal plant growth in the Humber Estuary during the relevant period.

97 Accordingly, without there being any need to adopt a position on whether, as the United Kingdom submits, the turbidity of the Humber Estuary lies behind the absence of accelerated growth of algae and higher forms of plant life in that estuary, it need only be stated that the Commission has not adduced at least a certain amount of evidence capable of proving that the enrichment of that estuary by nutrients led or could in the near future have led to such accelerated growth and that, therefore, it has not established that the second eutrophication criterion is fulfilled.

iii) The third and fourth eutrophication criteria: undesirable disturbance to the balance of organisms present in the water and to the quality of the water

98 The Commission contends that the Humber Estuary shows important indicators of eutrophication, such as high nutrient inputs from the catchments and elevated chlorophyll concentrations.

99 However, while such factors are capable of demonstrating, respectively, the existence of enrichment by nutrients and the existence of accelerated growth of algae and higher forms of plant life in the Humber Estuary, they are irrelevant on the other hand, as is already essentially clear from paragraph 39 of the present judgment, for the purpose of demonstrating the existence of undesirable disturbance to the balance of organisms present in the water or to the quality of the water.

100 In this connection, the Commission simply complains that the United Kingdom did not carry out the slightest quantitative evaluation of the occurrence of species indicative of eutrophication.

101 However, as has already been stated in paragraphs 42 to 48 of the present judgment, while the United Kingdom was obliged, under Directive 91/271, to identify the bodies of water that were eutrophic or liable to become so in the near future, the Commission has the task of proving the allegation that an obligation has not been fulfilled and, to that end, of adducing at least a certain amount of evidence of the – at least probable – adverse environmental effects caused by nutrient enrichment and accelerated growth of algae and higher forms of plant life.

102 With regard to such adverse effects, the Commission invokes, at most, first, the disappearance of Zostera in the Humber Estuary and, second, oxygen depletion and the development of algal toxins there.

103 So far as concerns, first, the effect on Zostera, while it is common ground that Zostera disappeared almost entirely from the Humber Estuary in the 1970s, the Commission adduces no specific and coherent evidence that its disappearance resulted, even probably, from the alleged accelerated growth of algae and higher forms of plant life caused by the enrichment of that estuary by nutrients, whereas the United Kingdom sets out, without moreover being contradicted in this regard, many alternative factors capable of being behind its disappearance.

104 The Commission in fact does no more than assert, in a general and abstract manner, that Zostera may be affected by nutrient enrichment and that, in the Humber Estuary, ‘it cannot be excluded’ that such enrichment is ‘at least partly’ to blame for its disappearance. However, the Commission adduces no specific evidence to this effect.

105 Thus, while the scientific contributions relied upon by the Commission in this connection in its reply (Davidson, D.M., and Hughes, D.J., Zostera Biotopes. An overview of dynamics and sensitivity characteristics for conservation management of marine SACs [Special Areas of Conservation], 1998, and Burkholder, J.M., et al., Seagrasses and eutrophication, 2007) reveal, respectively, that nutrient enrichment is ‘likely to’ cause eutrophication or that it constitutes ‘a major cause of seagrass disappearance worldwide’, they are general studies on the subject which do not in any way relate to the specific causes of the alleged decline of Zostera in the Humber Estuary in the relevant period and which, moreover, set out, by way of explanation of the decline of this type of bed, possible causes other than nutrient enrichment that has led to accelerated growth of algae and higher forms of plant life.

106 As has been noted in paragraph 46 of the present judgment, it is for the Commission to prove the causal link between the second and the third and fourth eutrophication criteria in each of the areas at issue.

107 In actual fact, the MV report, adduced by the Commission, states quite to the contrary, in the section concerning the Humber Estuary, that ‘it cannot be said that eutrophication is the positive cause of the decline of Zostera, or that the reduction in nutrient inputs would of itself result in a recovery’.

108 It is, admittedly, clear from the New Atlas of the British and Irish Flora, edited by C.D. Preston et al., 2002 (‘the new Preston atlas’), upon which the Commission relies in its reply, and from a scientific contribution adduced by it for the purpose of the hearing (Butcher, R.W., Zostera. Report on the Present Condition of Eel Grass on the Coasts of England, based on a Survey during August to October, 1933, 1941; ‘the 1933 Butcher study’) that Zostera was present in the Humber Estuary at certain times in the past.

109 However, such a past presence, which is moreover not disputed by the United Kingdom, is entirely irrelevant when examining the present complaint. Such a circumstance does not in any way demonstrate that the alleged disappearance of Zostera resulted from accelerated growth of algae and higher forms of plant life in the Humber Estuary that was caused by its enrichment by nutrients.

110 In particular, it follows from paragraphs 58 to 63 of the present judgment that a scientific study concerning the situation in the Humber Estuary in 1933, which was published in 1941, cannot possess decisive evidential value when determining whether that estuary had to be identified by the United Kingdom as an area sensitive to eutrophication as at 31 December 1993. Moreover, it is apparent from that study itself that multiple factors may be the cause of the disappearance of Zostera, as is contended by the United Kingdom in the present proceedings.

111 Furthermore, while the new Preston atlas, to which the Commission refers, shows that Zostera could have been present in the Humber Estuary until the 1970s, the atlas does not provide any indication as to its extent. The United Kingdom states without being contradicted in this regard by the Commission that it is apparent from the data provided by the study of M. Best (The occurrence (or presence) versus the prevalence of seagrasses (Zostera and Spartina spp) – an examination of evidence presented by the Atlas of British Flora, vascular plants database, Preston et al. 2002, Environment Agency, 2008; ‘the 2008 Best study’), which relates to the period from 1800 to 2007, that the presence of Zostera in that estuary has always been relatively sporadic.

112 In those circumstances, it appears all the less probable – and the Commission does not in any event adduce any evidence to the contrary – that the rareness of Zostera in the Humber Estuary during the relevant period resulted from an alleged accelerated growth of algae and higher forms of plant life caused by nutrient enrichment.

113 So far as concerns, second, oxygen depletion and the development of algal toxins, it is appropriate at the outset to reject the United Kingdom’s contention, expressed at the hearing, that it is apparent from recent data approved within the framework of OSPAR (Second OSPAR Integrated Report on the Eutrophication Status of the OSPAR Maritime Area, 2008; ‘the 2008 OSPAR report’) that there is an emerging consensus that the link between nutrient enrichment and the abundance of toxin-producing algae forming low-biomass blooms is not a parameter which is sufficiently indicative of the existence of a risk of eutrophication. In so far as that consensus reflects scientific and technical knowledge as it stood not on 31 December 1993 but at a much later time, it cannot be relevant in the present action, as follows from paragraphs 58 to 63 above.

114 That said, it must be found that the MV report, adduced by the Commission in support of its complaint, contradicts the Commission’s contentions since, according to that report, first, ‘it is unlikely that the depletion of oxygen, where it occurs, is a result of eutrophication within the estuary’ and, second, ‘algal toxins are not considered to be an issue on the English coast other than parts of the north-east coast’.

115 Nor does the Commission dispute the data supplied by the United Kingdom according to which continued monitoring of the Humber Estuary has shown no algal scums, no significant change in the overall composition and distribution of seabed invertebrate communities in the estuary and no increase or reduction in species variety.

116 Accordingly, it must be found that, even supposing that the existence of accelerated growth of algae and higher forms of plant life in the Humber Estuary may be considered proven, the Commission has not adduced at least a certain amount of evidence capable of proving that that accelerated growth produced as at 31 December 1993 or could in the near future have produced undesirable disturbance to the balance of organisms present in the water and to the quality of the water of that estuary.

117 Consequently, as the second, third and fourth eutrophication criteria have not been proved to the requisite legal standard, the first complaint must be rejected in so far as it relates to the Humber Estuary.

b) The Wash

118 A preliminary point to be made is that the United Kingdom is not correct in asserting that the Commission must demonstrate that the eutrophication criteria are met in relation to not only the Wash itself, but also to each of the four estuaries of the rivers, the Witham, the Welland, the Nene and the Great Ouse, which flow into it.

119 The United Kingdom itself explains in its report concerning the Wash supplied in response to the reasoned opinion of 19 April 2001 (Urban Waste Water Treatment Directive: Assessment of the Eutrophic Status of the Wash Embayment; ‘the United Kingdom report on the Wash’) that those four estuaries are part of the complex system formed by the Wash, a fact which is, moreover, confirmed by the various maps annexed to that report. On that basis, the Wash and those estuaries (collectively ‘the Wash’) must be considered to form a single body of water for the purposes of Directive 91/271.

i) The first eutrophication criterion: enrichment by nutrients

120 While the United Kingdom asserts that enrichment of the Wash by nutrients has decreased significantly in recent years, it does not dispute that during the relevant period there was such enrichment, as indicated by the data in the ERM report adduced by the Commission.

121 In any event, the United Kingdom cannot legitimately submit in this regard that, since sewage treatment works contribute less than 5% of nitrogen inputs to the Wash, the identification of that body of water as a sensitive area would entail disproportionate expenditure in that it necessitates more stringent treatment of urban waste water. It is settled case-law that a Member State cannot plead practical or administrative difficulties to justify failure to comply with obligations and time-limits laid down by a directive. The same holds true of financial difficulties, which it is for the Member States to overcome by adopting appropriate measures (see, inter alia, Case C-433/02 Commission v Belgium [2003] ECR I‑12191, paragraph 22, and the judgment of 30 November 2006 in Case C-293/05 Commission v Italy, paragraph 35).

122 It is likewise necessary to reject the United Kingdom’s contention that enrichment by nitrogen is more effectively addressed through measures taken pursuant to Council Directive 91/676/EEC of 12 December 1991 concerning the protection of waters against pollution caused by nitrates from agricultural sources (OJ 1991 L 375, p. 1). A Member State cannot avoid complying with Directive 91/271 on the ground that it observes Directive 91/676, since the latter, being intended to reduce and prevent water pollution caused or induced by nitrogen from agricultural sources (Standley and Others, paragraph 35), does not affect, inter alia, the enrichment of water by phosphorus, which Directive 91/271 seeks to remedy amongst other matters. The United Kingdom does not contest the findings of the ERM report that phosphorus inputs also lie behind the enrichment of the Wash by nutrients.

123 The first eutrophication criterion is therefore proven as regards the Wash.

124 Accordingly, it remains to be examined whether the Commission has proved to the requisite legal standard that the three other eutrophication criteria are also fulfilled as regards that area at issue.

ii) The second eutrophication criterion: an accelerated growth of algae and higher forms of plant life

125 According to the Commission, the scientific data contained in the ERM report show that the enrichment of the Wash by nutrients has led to accelerated growth of algae and higher forms of plant life in the Wash. It states that such growth is attested by the exceeding of the chlorophyll concentration threshold of 10 μg/l and by the existence of substantial beds of macroalgae in that area.

126 So far as concerns, first, the chlorophyll concentration level, it is necessary at the outset to dismiss as irrelevant to examination of the present action, in accordance with what has been stated in paragraphs 58 to 63 above, the data in Eastern English Coast, 2007 – a report which the Commission relies upon in its reply – inasmuch as in that report the United Kingdom gave the Wash a ‘+’ rating for chlorophyll. Since this report concerns the period from 1999 to 2006, it has no probative value in the present action.

127 The United Kingdom is also justified in asserting that the threshold of 15 μg/l for the 90th percentile (under which the existence of accelerated growth of algae and higher forms of plant life is demonstrated where the threshold is exceeded by the ninth sample out of ten ranked in increasing order), a threshold accepted by the United Kingdom in 2007 within the framework of OSPAR and relied upon by the Commission in its reply, cannot be adopted when assessing the merits of the present action. Since the United Kingdom has stated, without being contradicted in this regard, that that method of assessment was not applied as at 31 December 1993, it being designed to identify eutrophic waters within the framework of OSPAR from 2007, it cannot possess any relevance in this action.

128 It must, however, be stated with regard to the chlorophyll concentration level measured in the Wash that, according to the ERM report adduced by the Commission, the Great Ouse Estuary had, between 1987 and 1992, ‘levels … above 10 [μg/l] throughout this period with peaks ranging between 100-200 [μg/l]’. Furthermore, it is apparent from a study adduced by the Commission with its reply (Rendell, A.R., et al., Nutrient Cycling in the Great Ouse Estuary and its Impact on Nutrient Fluxes to the Wash, England, 1997; ‘the 1997 Rendell study’) that very high chlorophyll concentrations, ranging from 40 μg/l to 190 μg/l, were recorded in that estuary throughout the growing season between March and September 1993.

129 Moreover, while the data mentioned in this regard by the ERM report in respect of the Wash disclose a chlorophyll concentration level that is in general not so high, the fact remains that, according to that report, the level exceeded the 10 μg/l threshold in that area, in particular in its southern section, in 1993, in both June (11 μg/l) and September (23 and 33 μg/l), and in June 1994 (between 10 and 15.1 μg/l).

130 It follows that, as the ERM report notes, during the relevant period the chlorophyll concentration levels recorded in the Wash regularly exceeded in the summer, sometimes substantially, the 10 μg/l threshold, a threshold which, as is apparent from paragraphs 75 to 78 of the present judgment, is liable to indicate accelerated growth of algae and higher forms of plant life. In any event, contrary to what is asserted by the United Kingdom, the chlorophyll concentration levels above that threshold that have been recorded cannot, given their repeated occurrence, be considered to be ‘exceptional peaks’.

131 The arguments and evidence put forward by the United Kingdom are not such as to affect these findings.

132 As regards, first, the contention that the data provided in the United Kingdom report on the Wash show that the mean chlorophyll concentration level there did not exceed the 10 μg/l threshold between 1992 and 2000, it must be stated that those data do not call into question the chlorophyll concentration levels indicated in the ERM report for the Great Ouse Estuary and that the United Kingdom report on the Wash acknowledges itself that, between 1995 and 1997, a not insignificant portion of the samples taken, that is to say, in essence, between 20% and 35% of them, revealed that the 10 μg/l threshold was exceeded, including in summer.

133 Moreover, it is noted in this regard in the MV report that, according to the data provided in the United Kingdom report on the Wash, the mean chlorophyll concentration levels recorded in the summers of 1995 and 1996 were, in the case of the Nene Estuary, of the order of 40 μg/l mid-estuary, with peaks above 100 μg/l, and, in the case of the Welland Estuary, at least 30 μg/l mid-estuary, with peaks close to 100 μg/l.

134 As regards, second, the contention that the high chlorophyll levels referred to in the ERM report concern the less saline freshwater sections of the Wash, in which a chlorophyll concentration level of 100 μg/l may be regarded as normal, it is to be observed that, even if such a level can be accepted as a maximum concentration in the freshwater sections of the estuaries, the ERM report, citing the 1997 Rendell study, refers to levels substantially higher than that level of 100 μg/l, since it states that levels of up to 189 μg/l were recorded in the less saline areas of the Great Ouse Estuary. The United Kingdom cannot therefore contend that the data in the 1997 Rendell study accord with its proposition.

135 Nor, third, is it possible to uphold the contention that the hydrodynamic conditions of the Wash are not conducive to accelerated growth of algae and higher forms of plant life, in particular because of the natural turbidity of both the embayment and the estuaries.

136 The ERM report and the MV report, taking up the results of the 1997 Rendell study, expressly state in this regard that high chlorophyll concentration levels, reaching, as the case may be, 36 μg/l, 55 μg/l and even 114 μg/l, were observed in March and June 1992 in the most turbid parts of the Great Ouse Estuary, thus testifying to significant phytoplankton growth in those areas at a time close to the relevant period, notwithstanding the turbid conditions. According to the 1997 Rendell study, maximum chlorophyll concentration levels regularly observed in the spring and summer months that are so high can be explained ‘in terms of the rapid movement of phytoplankton throughout the water column … and their adaptation to the low light regime … which permit net primary production, despite the turbid conditions’.

137 Besides, the regularly high chlorophyll concentration levels in the Wash which are noted in the ERM report tend to indicate that any turbidity of that body of water is not actually such as to prevent accelerated phytoplankton growth. The United Kingdom indeed does not appear truly to deny this fact, since in this regard it does no more than prudently maintain that ‘the extent of algal growth is constrained and there are unlikely to be large scale and widespread algal blooms causing an undesirable disturbance’, thereby contesting fulfilment of the third and fourth eutrophication criteria more than the second criterion.

138 Accordingly, the data provided by the Commission concerning the chlorophyll concentration level in the Wash can be considered to be indicative of a certain accelerated growth of algae and higher forms of plant life in that area at issue.

139 So far as concerns, second, the presence of macroalgae, it is apparent from the ERM report that no systematic study has been carried out on this subject. However, the Commission relies upon the passage in that report indicating that the presence of macroalgae beds covering an extensive area was noted in the region of the Welland Estuary in 1997. The Commission also refers to the fact that the OSPAR Commission had already found in 1993 that there were changes in macrophyte growth, notably in the form of mass occurrence of Ulva, in the Wash, due to long-term increasing anthropogenic eutrophication in these coastal waters.

140 While the United Kingdom, referring to the United Kingdom report on the Wash, disputes the presence of macroalgae in that area, it restricts itself in this regard to assertions that are not backed up by documented scientific sources, except so far as concerns the years 2000 to 2002, for which it refers to a survey carried out by the Environment Agency. However, that period is not relevant in the present action. For the same reason, the United Kingdom cannot challenge the data in the ERM report by relying on the report Eastern English Coast referred to in paragraph 126 of the present judgment, as this report concerns the period between 1999 and 2006.

141 It is nevertheless to be noted that the evidence adduced by the Commission concerning the presence of macroalgae in the Wash does not include any figures that can provide support for the extent of coverage that is alleged. First, the statement in the ERM report that is referred to in paragraph 139 of the present judgment not only is not based on direct observation but also is fragmentary. That statement, which results merely from a telephone conversation with an officer of English Nature, the public body which was responsible for nature protection in England, concerns a single year in the relevant period and just one of the Wash estuaries. Second, the findings attributed to the OSPAR Commission in 1993 do not appear in the monitoring report of the Centre for Environment, Fisheries and Aquaculture Science (‘CEFAS’) that is contained in the May 2003 edition of Shellfish News to which the Commission refers in its application.

142 However, for the purposes of the examination relating to the second eutrophication criterion, it is to be accepted that these few isolated pieces of evidence adduced by the Commission, testifying to the presence of macroalgae in the Wash during the relevant period, taken together with the greater body of specific and coherent evidence concerning the regular recording of high chlorophyll concentration levels in that area at issue during the relevant period, including in summer, demonstrate to the requisite legal standard that there was accelerated growth of algae and higher forms of plant life in that area during that period, accelerated growth which indeed was not contested by the United Kingdom in its response to the reasoned opinion of 19 April 2001.

143 Therefore, as the United Kingdom has adduced nothing capable of calling into question the conclusions of the ERM report that that growth was caused by the enrichment of the Wash by nutrients, the Commission has proved to the requisite legal standard that the second eutrophication criterion is fulfilled so far as concerns this area at issue.

iii) The third and fourth eutrophication criteria: undesirable disturbance to the balance of organisms present in the water and to the quality of the water

144 The Commission submits, first, that it is apparent from the data provided by the United Kingdom itself that the relevant English coastal waters, that is to say the Humber to Norfolk subdivision, which includes the Wash, are extremely enriched by nutrients. Furthermore, chlorophyll concentration levels in the Wash have frequently and considerably exceeded the 10 µg/l threshold. According to the Commission, the MV report showed in this connection unexpectedly high levels of phytoplankton growth despite the high turbidity. This results in oxygen super-saturation in all the Wash estuaries. Nor have the United Kingdom authorities adduced any evidence that the low level of dissolved oxygen recorded in the Wash has no environmental impact.

145 It is clear, however, that, while those circumstances may demonstrate that the first and second eutrophication criteria are fulfilled in the area at issue, they do not, on the other hand, enable it to be ascertained whether the third and fourth criteria are too.

146 It is true that oxygen super-saturation or deoxygenation, which, according to the ERM report, constitute contradictory tendencies liable to appear in parallel in eutrophic waters, might produce an undesirable disturbance to the balance of organisms present in the water (see, by analogy, Commission v France, paragraphs 44 and 54). However, the Commission has adduced no specific evidence capable of demonstrating the existence of such disturbance in the present case.

147 In this regard, the Commission cannot profitably complain that the United Kingdom authorities have not proved that the low level of dissolved oxygen recorded in the Wash has no environmental impact. As has been stated in paragraphs 42 to 48 of the present judgment, it is incumbent upon the Commission, which has the burden of proving the allegation that an obligation has not been fulfilled, to adduce at least a certain amount of evidence that the eutrophication criteria were fulfilled so far as concerns the area at issue as at 31 December 1993 or that it was probable that they would be in the near future. It is only if such evidence has been furnished by the Commission that the Member State concerned must, in turn, rebut the Commission’s case by adducing any evidence relevant for that purpose.

148 Second, the Commission states that an atypical form of diarrhetic shellfish poisoning (‘DSP’) has been identified in Wash cockles, which has resulted in Wash shellfishery closures.

149 However, the cases of DSP relied upon by the Commission, which were revealed by the study results mentioned in the MV report and by the CEFAS monitoring reports contained in the May 2003 and May 2005 editions of Shellfish News, concern the years 2002 to 2005, that is to say a period considerably after the relevant period. Therefore, in accordance with paragraphs 58 to 63 of the present judgment, any harmful environmental effects thus recorded in those reports cannot have probative value in the present action.

150 Third, the Commission states that the Wash has known extensive blooms of Phaeocystis. It maintains that in certain circumstances the demonstration of accelerated growth of a species of phytoplankton such as Phaeocystis is in itself direct evidence of undesirable change, because different ambient nutrient concentrations result in different species assemblages. Thus, Phaeocystis is known for producing, in high concentrations, the appearance of a mass of viscous foam which covers the surface of the water and washes up on the coast or clogs fishing nets. The Commission adds that this species is recognised by OSPAR as harmful since it is distasteful to the zooplankton which the fish feed on and its blooms can cause foam on beaches. According to the Commission, the United Kingdom, however, appears relatively unconcerned about the presence of those blooms.

151 It is to be noted with regard to those submissions that, as has already been stated in paragraph 38 of the present judgment, proof of an accelerated growth of algae and higher forms of plant life, which constitutes the second eutrophication criterion, cannot, as such, be considered to demonstrate an undesirable disturbance to the balance of organisms present in the water, or indeed to the quality of the water, which correspond to the third and fourth eutrophication criteria.

152 It is true that the Court has already held, first, that modification of the structure of the phytoplankton community so as to reinforce the presence of a species such as Phaeocystis, which, while not toxic, is none the less harmful, constitutes an undesirable disturbance to the balance of organisms present in the water and, second, that changes to the colour, odour and texture of the water, whose adverse effects on tourist activities are obvious, and which in addition are very likely to have harmful effects on fishing activities, represent an undesirable disturbance to the quality of the water (see, to this effect, Commission v France, paragraphs 23, 38, 55 and 56).

153 In the present case, however, although the 1997 Rendell study, which relates to surveys carried out between 1992 and 1994, indicates that enrichment of the Wash by nutrients ‘may affect primary production in coastal waters by contributing to the shift in species dominance from diatoms to flagellates and affecting the likelihood of bloom conditions occurring during the summer months’, the Commission has not adduced any specific evidence attesting that there were Phaeocystis blooms in the Wash during the relevant period.

154 While the ERM report, upon which the Commission essentially relies, mentions that in 1989 very high chlorophyll concentration levels were associated with extensive blooms of Phaeocystis, this statement concerns the southern North Sea and not the Wash. That report itself observes with regard to the Wash that instances of foam on beaches are rare.

155 Similarly, the Commission cannot deduce any reliable evidence from the study, relied upon in its reply, by P. Shaw and D. Purdie (Phytoplankton photosynthesis-irradiance parameters in the near-shore UK coastal waters of the North Sea: temporal variation and environmental control, 2001), since that study, though relating to surveys carried out between 1993 and 1995, concerns the presence of Phaeocystis in the coastal waters of the North Sea.

156 As to the remainder, the Commission merely states that the chlorophyll concentration peaks observed in the Wash are consistent with Phaeocystis blooms. However, a general and abstract contention of that kind concerning the possible link between the chlorophyll level and the presence of that species of phytoplankton does not demonstrate in the slightest that there were in fact such blooms in the Wash during the relevant period.

157 With regard to the Commission’s contention that the United Kingdom has not studied the composition of the phytoplankton sufficiently, for example by failing to analyse sediment cores, it need only be reiterated that, as stated in paragraphs 42 to 48 of the present judgment, it is for the Commission to prove the allegation that an obligation has not been fulfilled, by adducing at least a certain amount of evidence that the eutrophication criteria were fulfilled in the area at issue as at 31 December 1993 or that it was probable that they would be in the near future; it is only if such evidence has been furnished that the Member State concerned must, in turn, rebut the Commission’s case by adducing any evidence relevant for that purpose. In the present case, as has already been pointed out, the Commission has not adduced any evidence that Phaeocystis blooms were present in the Wash during the relevant period.

158 In any event, even if such evidence had been adduced, inasmuch as the United Kingdom submitted, without being contradicted in that regard, that limited incidence of foam on United Kingdom beaches is longstanding and has been recorded for over a century, it was for the Commission, which bears the burden of proof so far as concerns the causal link between the second eutrophication criterion and the third and fourth criteria, to demonstrate that the alleged instances of the presence of foam result, even probably, from accelerated growth of algae and higher forms of plant life caused by nutrient enrichment.

159 In this connection, the Commission cannot profitably rely on the fact that there is increased recognition in the scientific community of the link between the frequency of occurrence of blooms of algae, including those forming scum, such as Phaeocystis, and increased nutrient inputs, a link which it states to be confirmed by the 2008 OSPAR report which it produced at the hearing. Such a conclusion does not amount to specific evidence of the existence of such a link as regards the Wash. Furthermore, in so far as that conclusion does not seem to reflect scientific and technical knowledge as it stood on 31 December 1993, it cannot, as is apparent from paragraphs 58 to 63 above, be relevant in the present action.

160 Fourth, the Commission relies on the presence in the Wash of substantial beds of macroalgae such as Ulva (‘green tides’). It states that the United Kingdom did not carry out any study to measure the density of those algae and to demonstrate that a healthy benthos existed in and on the sediment.

161 It is necessary first of all to reiterate that it is true that, as the United Kingdom submits, and as has already been stated in paragraph 38 of the present judgment, proof of an accelerated growth of algae and higher forms of plant life, which constitutes the second eutrophication criterion, cannot, as such, be considered to demonstrate undesirable disturbance to the balance of organisms present in the water or to the quality of the water, which correspond to the third and fourth eutrophication criteria.

162 However, as the Court has already held, the proliferation of macroalgae such as Ulva, which are opportunistic algae, constitutes an undesirable disturbance to the balance of organisms present in the water and, because of their adverse effects inter alia on tourist activities, green tides also constitute an undesirable disturbance to the quality of the water. Those algae, which are easily torn from their substrate and ultimately wash up on beaches, often covering them to some depth, strongly disturb or even render impossible tourist activities such as bathing, fishing or hiking along the coast (see, to this effect, Commission v France, paragraphs 23, 73 and 74).

163 In the present case, it must nevertheless be stated, first, that while, as is apparent from paragraph 142 above, the Commission has admittedly adduced certain isolated pieces of evidence capable of suggesting that macroalgae were present in the Wash or, at least, in a part of it, evidence which, taken together with the high chlorophyll concentration levels, can demonstrate that the second eutrophication criterion is established so far as concerns that area at issue, it has not adduced evidence showing that their presence was significant and, therefore, corresponded to a genuine proliferation.

164 In this regard, the MV report, adduced by the Commission in support of its argument, indeed does no more than state that green macroalgae were abundant in the Wash at the beginning of the 20th century, that is to say, well before the relevant period. Furthermore, while that report indicates that it cannot be asserted that green algae will not proliferate to dangerous levels given the current enrichment of that body of water by nutrients, the hypothesis of a proliferation is not, however, backed up by any scientific data that are specific and quantified.

165 It must be stated, secondly, that the Commission has not adduced any evidence that the alleged presence of Ulva in the Wash, even though it was limited, resulted in significant adverse environmental effects. The Commission, which has the burden of proving the allegation that an obligation has not been fulfilled, cannot merely complain that the United Kingdom did not carry out the necessary studies in order to demonstrate the absence of such adverse effects, as otherwise the burden of proof would effectively be reversed. In any event, the Commission has not contested the United Kingdom’s assertion, derived from the United Kingdom report on the Wash, that the benthic invertebrates associated with the sediment are healthy, a 15-year data set indicating a normal community which changes according to salinity regime and sediment characteristics.

166 Fifth and finally, the Commission mentions the disappearance of Zostera in the Wash as a possible result of eutrophication. It submits that the effect of eutrophication on Zostera is a well-established phenomenon. Historical publications from the beginning of the 20th century and later prove the abundance of macroalgae and also a certain occurrence of Zostera species. The wasting disease referred to by the United Kingdom to explain their disappearance did not affect Zostera noltii and the susceptibility of Zostera marina to that disease is increased by elevated nitrogen concentrations. The Commission adds that, although the United Kingdom specifies many factors as possible causes of the disappearance of Zostera, it appears not to be concerned that one of the main causes is the exposure of Zostera to excess nutrient enrichment and high ammonia levels.

167 Those contentions must, however, be rejected for the same reasons as those in paragraphs 103 to 112 of the present judgment concerning the Humber Estuary.

168 The Commission does not adduce any specific evidence that the slight presence of Zostera in this area at issue results, at least probably, from the accelerated growth of algae and higher forms of plant life caused by nutrient enrichment. It does no more than assert in a general and abstract manner that Zostera may be affected by such circumstances and that its disappearance is ‘a possible result of eutrophication’.

169 It is true that the Commission maintains that it is apparent from the new Preston atlas and from other information, in particular an address cited in the MV report which was given in 1966 by Mr R. Pilcher to the Lincolnshire Naturalists Society, that Zostera may have been present in greater quantity in the Wash during the first part of the 20th century.

170 However, that earlier presence, which is moreover not disputed by the United Kingdom, is irrelevant since it does not in any way demonstrate that the alleged disappearance of Zostera resulted, at least probably, from accelerated growth of algae and higher forms of plant life in the Wash that was caused by its enrichment by nutrients.

171 Furthermore, it is apparent from the MV report, adduced by the Commission itself, that Zostera was never present in the Wash in abundance. While the new Preston atlas, also adduced by the Commission, shows that Zostera could in fact have been present in the Wash until the 1970s, or even until 1986, the atlas does not provide any indication as to its extent. The United Kingdom states, without being contradicted in this regard by the Commission, that it is apparent from the data provided by the 2008 Best study concerning the period from 1800 to 2007 that the presence of Zostera in the Wash has always been relatively sporadic.

172 In the light of the foregoing, it must be found that the Commission has not adduced at least a certain amount of evidence capable of proving that the accelerated growth of algae and higher forms of plant life in the Wash produced or might in the near future have produced in that area at issue undesirable disturbance to the balance of organisms present in the water and to the quality of the water.

173 Consequently, as the third and fourth eutrophication criteria have not been proved to the requisite legal standard so far as concerns the Wash, the first complaint must be rejected in so far as it relates to that area at issue.

c) The Deben and Colne Estuaries

i) The first eutrophication criterion: enrichment by nutrients

174 While the United Kingdom submits that enrichment of the Deben and Colne Estuaries by nutrients has decreased significantly in recent years, it does not dispute that during the relevant period there was such enrichment, as indicated by the data in the ERM report adduced by the Commission.

175 The United Kingdom’s argument that enrichment by nitrogen is more effectively addressed through measures taken pursuant to Directive 91/676 must be rejected for the same reasons as those stated in paragraph 122 of the present judgment in respect of the Wash.

176 The first eutrophication criterion is therefore proven for the Deben and Colne Estuaries.

177 Accordingly, it must be examined whether the Commission has proved to the requisite legal standard that the three other eutrophication criteria are fulfilled as regards these areas at issue.

ii) The second eutrophication criterion: an accelerated growth of algae and higher forms of plant life

178 Since it is common ground that the Deben and Colne Estuaries form separate bodies of water, the situation of each of these estuaries with regard to the second eutrophication criterion should be examined separately.

– The Deben Estuary

179 According to the Commission, it is apparent from the ERM report that nutrient inputs, essentially from sewage treatment works, have resulted in accelerated growth of algae and higher forms of plant life in the Deben Estuary. It relies in this regard on the growth of phytoplankton and on macroalgal coverage.

180 So far as concerns, first, phytoplankton growth, it must be stated that although, as already indicated in paragraph 127 of the present judgment, the Commission cannot validly rely on exceeding of the chlorophyll concentration threshold of 15 μg/l for the 90th percentile, a threshold accepted by the United Kingdom within the framework of OSPAR, it is apparent from the ERM report, which is based in this regard on the ‘1994 Elliott report’, that this estuary experienced very high chlorophyll concentration peaks, reaching 86.6 µg/l in 1992 and, in particular, 339 µg/l in 1993. The United Kingdom is wrong in its assertion that the Commission did not take into consideration the duration and extent of phytoplankton growth and what takes place throughout the year. The ERM report expressly states that those peaks occurred from spring until autumn.

181 While the United Kingdom seeks to contest the data in the ERM report, the material which it puts forward in this regard, namely the results of a study carried out by the Environment Agency which are set out in the report relating to the Deben and Colne Estuaries provided in response to the reasoned opinion of 19 April 2001 (Urban Waste Water Treatment Directive: Assessment of the Eutrophic Status of the Deben and the Colne Estuaries; ‘the United Kingdom report on the Deben and Colne Estuaries’), confirms the conclusions of the ERM report, since it attests to the presence between 1992 and 1997 of algal blooms involving chlorophyll concentration levels exceeding 10 µg/l and to values in excess of that threshold also in the summer months at the most upstream sites of the two estuaries concerned. The United Kingdom report on the Deben and Colne Estuaries states in addition that those estuaries have saline waters in their middle and outer sections, a fact which justifies the threshold of 10 µg/l being regarded as a relevant criterion. According to the report, this threshold was also exceeded in those sections in summer.

182 Nor can the United Kingdom, in order to contest the data in the ERM report, pr