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2.4.2.      Lake water bodies

There are more than 500 000 natural lakes larger than 0.01 km² (1 ha) in Europe (EEA 1995). About 80 % to 90 % of these are small with a surface area of between 0.01 and 0.1 km², whereas around 16 000 have a surface area exceeding 1 km². Twenty four European lakes have a surface area larger than 400 km².

Many natural European lakes appeared 10 000 to 15 000 years ago; when the ice sheet covered all of northern Europe. In central and southern Europe ice sheets only stretched as far as mountain ranges. As a rule, the regions comprising many natural lakes were affected by the Weichsel ice. For example, countries like Norway, Sweden, and Finland have numerous lakes that account for approximately 5% to 10% of their national surface area. In central Europe, most natural lakes lie in mountain regions. Lakes at high altitude are relatively small whereas those in valleys are larger, for example Lac Léman, Bodensee, and Lago Maggiore in the Alps. European countries which were only partially affected by the glaciation period (Portugal, Spain, France, Belgium, southern England, central Germany, the Czech Republic, and the Slovak Republic) have few natural lakes. In these areas man-made lakes such as reservoirs and ponds are often more common than natural lakes.

Lakes are often split into two main types (shallow and deep lakes) as they tend to have different sensitivities to pressures such as water pollution. High quality shallow lakes are characterised by healthy submerged plant communities and associated diverse communities of invertebrates, fish and wetland birds. Phytoplankton is also present but typically in low levels. Naturally characterised by clear water, these systems have frequently shifted into turbid, phytoplankton-dominated states lacking macrophytes, primarily caused by nutrient pollution (eutrophication). Deep lakes are mainly found in mountainous regions and under natural conditions they are characterised by very low nutrient loads. Macrophytes are restricted to a narrow belt along the shores and phytoplankton abundance is low. Eutrophication in deep lakes causes enhanced primary production by phytoplankton, in severe cases algal blooms and oxygen depletion (particularly in the deep zones) may affect all processes and species

Twenty-one Member States have reported lakes. In total around 18 000 lake water bodies with an area greater than 90 000 km² has been reported by Member States. Two countries, Sweden, and Finland, reported more than two thirds of the lake water bodies and lake area.

The average area of the more than 18 000 reported lake water bodies is 5.1 km² – the average size is markedly influenced by the very large lakes. Seven Member States (Austria, Estonia, France, Greece, Hungary, Lithuania, and Spain) had average size of lake water bodies greater than 10 km².

Half of the reported lakes are less than 1 km² in area and more than 87 % of the reported lake water bodies have an area less than 5 km² (Table 2.7) Only 78 of the reported lake water bodies have an area greater than 150 km²; Finland and Sweden have reported 28 and 16 lake water bodies greater than 150 km², and Lithuania and Spain reported 9 and 8 large lake water bodies.

 Table 2.7: Number of lake water bodies according to size of WBs

Some Member States (e.g. Sweden and Finland) have divided their large lakes into several water bodies, while other Member States (e.g. Austria) only have one water body for each of their lakes.