ABSTRACT1. The European Water Framework Directive requires the determination of ecological status in European fresh and saline waters. This is to be through the establishment of a typology of surface water bodies, the determination of reference (high status) conditions in each element (ecotype) of the typology and of lower grades of status (good, moderate, poor and bad) for each ecotype. It then requires classification of the status of the water bodies and their restoration to at least 'good status' in a specified period.2. Though there are many methods for assessing water quality, none has the scope of that defined in the Directive. The provisions of the Directive require a wide range of variables to be measured and give only general guidance as to how systems of classification should be established. This raises issues of comparability across States and of the costs of making the determinations.3. Using expert workshops and subsequent field testing, a practicable pan-European typology and classification system has been developed for shallow lakes, which can easily be extended to all lakes. It is parsimonious in its choice of determinands, but based on current limnological understanding and therefore as cost-effective as possible.4. A core typology is described, which can be expanded easily in particular States to meet local conditions. The core includes 48 ecotypes across the entire European climate gradient and incorporates climate, lake area, geology of the catchment and conductivity.5. The classification system is founded on a liberal interpretation of Annexes in the Directive and uses variables that are inexpensive to measure and ecologically relevant. The need for taxonomic expertise is minimized.6. The scheme has been through eight iterations, two of which were tested in the field on tranches of 66 lakes. The final version, Version 8, is offered for operational testing and further refinement by statutory authorities.

In the eutrophic Lake Võrtsjärv (Central Estonia, area 270 km 2 , mean depth 2.8 m) rotifers form ca. 90% of total abundance and 80% of biomass in winter zooplankton community. The winter rotifer assemblage was dominated by Polyarthra dolichoptera, both in abundance and in biomass. Synchaeta verrucosa and Keratella quadrata were the subdominants. Thus, winter rotifer community had low diversity and high dominance of a few species. This pattern probably refers to the period of extreme environmental conditions where the rotifer assemblage is composed of few well-adapted species, and the low diversity here was not indicating instability of community structure, but the scarcity of suitable niches. These community structure indices indicate that the winter rotifer assemblage of L. Võrtsjärv was very similar to autumn assemblage, but very different from the spring one. In winter, small raptors were the most important functional group. The second place is occupied by larger raptors. Marginal role of fine particle sedimentators, absence of suckers and high proportion of large raptors were contrasting features of the winter trophic structure in comparison with the other seasons. Changes have taken place in the winter rotifer assemblage in L. Võrtsjärv in 1990Võrtsjärv in -2007 Against the background of diminishing rotifer abundance, the dominant species has become even more prevalent, and the diversity of the winter rotifer assemblage has decreased. Shifts in the community trophic structure were also observed.

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Lake Peipsi-Pihkva (3555 km2 , mean depth 8 .3 m), consisting of three parts, (L . Peipsi, L . Pihkva, L . Lammijarv) is located on the border of Estonia and Russia . L . Peipsi belongs to unstratified eutrophic lakes with mesotrophic features, L. Lammijarv has some dyseutrophic features, while L . Pihkva is strongly eutrophic . The total annual nutrient load is 15 .57 tons N km -2 and 327 kgP km -2 with 74% of N and 39% of P originating from agriculture . The mean concentrations of total N and P in the lake are 876 mg m -3 and 46 mg m-3, respectively, both being the highest in L . Pihkva and the lowest in the northern part of L . Peipsi . Average pH is 8 .14 and Secchi disk transparency 1 .63 m . Diatoms and blue-green algae prevail in phytoplankton biomass . The blue-greens Gloeotrichia echinulata and Aphanizomenon flos-aquae dominate in summer causing the water-blooms . The concentration of Chla was the lowest in the northern part of L . Peipsi (mean 14 .7 mg m -3 ) and the highest in the southern part of L . Pihkva (mean 47 .9 mg m -3 , median 16 .3 mg m-3 ) . An increase of Chla and decrease of Secchi depth could be noticed in 1983-1988, while in 1988-1994 the tendency was opposite . The long-term average primary production is 0 .8 g C m-2 d -1 . Zooplankton is remarkably rich in species, the average biomass in the vegetative period being 2-3 g m-3 and production 22 g C m -2 . The role of rotifers in production is 53% followed by that of cladocerans (30%), copepods (16%) and Dreissena polymorpha larvae (1%) . The total count of bacteria is 1-9 million cells per ml . Chironomus plumosus and Potamothrix hammoniensis are dominating in the profundal . The average abundance of macrozoobenthos (without big molluscs) 2617 ind . m -2 , and their biomass 12 .34 g m -2 are considered to be the highest among the large lakes of North Europe . Macroflora occupies a small percentage of the total lake area but is rich in species . Taxa forming communities are Potamogeton perfoliatus, Phragmites australis, Schoenoplectus lacustris, Potamogeton lucens, Eleocharis palustris, and Polygonum amphibium . Submerged vegetation occupies the first place amongst different growth forms, followed by emergent plants . The main commercial fishes are lake smelt, perch, ruff, roach, bream, pike, vendace and pikeperch. The stock of vendace has sharply decreased in the last years, while the amount of pikeperch has increased . Considering annual fish catches (9000-12000 tons or 25-34 kg ha-1 ), L . Peipsi-Pihkva exceeds all large lakes in North Europe .

The effect of damming on the structure of the macroinvertebrate community and biological quality was studied in nine (the 3-6th order) lowland streams of Estonia, Central-Baltic ecoregion of Europe. Four habitats-reservoirs with accumulated fine sediments, reservoirs with hard bottom, and two corresponding below-dam areas (both fast-flowing)-were compared to study whether and how significantly the bottom substrata in dammed areas affected macroinvertebrates and biological quality downstream of dams. The standard kick-net samples (1.25 m 2 , complemented with qualitative sample) were collected in autumn 2005-spring 2006. The multimetric biological quality, based on five macroinvertebrate indices (total taxa richness, EPT taxa richness, Average Score Per Taxon, Danish Stream Fauna Index, Shannon diversity) was estimated and compared with reference values. Biological quality in reservoirs with hard bottom and their downstream reaches corresponded to good, or even high quality. Conversely, damming affected biological quality significantly and negatively, above the dam if fine sediments were accumulated. The effect was the strongest within muddy reservoirs themselves (revealing moderate quality only). However, some harmful consequences of mud were observed also downstream of dams. The results also demonstrated that the indices of estimation of organic pollution and/or general quality were able to reflect significant changes in stream flow. The definition procedure of surface water bodies and the list of the surface water bodies that require status estimation; status classes of surface water bodies and the corresponding values of quality metrics; and the estimation procedure of status classes. Regulation of Estonian Minister of