Planktonic algae and zooplankton are abundant in the water column, submerged vegetation is diverse and numerous species of invertebrate and fish are present. Plant assemblages differ according to geographical area and nutrient concentration but some plant species such as Potamogeton pectinatus (fennel-leaved pondweed) and Myriophyllum spicatum (spiked water-milfoil) are characteristic throughout the UK. Common floating-leaved plants include Nuphar lutea (yellow water lily) and there is often a marginal fringe of reedswamp, which is an important component of the aquatic ecosystems. Bottom-dwelling invertebrates such as snails, dragonflies and water beetles are abundant and calcareous sites may support large populations of the native freshwater white-clawed crayfish (Austropotamobius pallipes). Fish such as roach (Rutilus rutilus), tench (Tinca tinca) and pike (Esox lucius) are typical of eutrophic standing waters, but salmonids also occur naturally in some. Amphibians, including the UK BAP species great crested newt (Triturus cristatus), are often present and the abundance of food can support internationally important bird populations. Lakes change naturally over time, slowly filling in with silt and vegetation and usually, in the absence of human impact, gradually becoming less fertile.
In the UK, eutrophic waters are most typical of hard water areas of the lowlands of southern and eastern Britain, but they also occur in the north and west, especially near the coast. There are currently no accurate estimates of the amount of eutrophic standing water in the UK but some estimates place the area at around 1785 km2. The distribution of eutrophic lakes in the UK can be seen at http://www.jncc.gov.uk/publications/JNCC312/habitat.asp?FeatureIntCode=H3150.
There are many factors which are affecting eutrophic lakes such as:
- Climate Change: A rise in temperature would favour more rapid plant growth and changes in water supply would also have a negative impact on smaller or more sensitive water bodies
- Pollution causing Eutrophication: Pollution from both point and diffuse sources leads to an increased nutrient load on the water body, therefore increasing plant growth and ultimately leading to decreased dissolved oxygen
- Changes in Land Use: Changes in land cover can release nutrients from the soil and cause increased siltation which may smother spawning areas. Also, the removal of waterside vegetation such as reedswamp can increase the amount of siltation and nutrients entering the water body.
- Altering the Biotic Community: Removal of fish predators and/or increasing the number of bottom dwelling fish may increase turbidity, therefore increasing the amount of nutrients being released from sediments. Also the manipulation of fish stocks for fishing may affect invertebrate and plant communities.
- Recreation: The use of standing water bodies for recreational activities may disturb bird populations as well as increasing turbidity. Damage to reedswamp may occur also and increased pollution from equipment such as boats will also adversely affect the habitat.
Approximately 200 eutrophic standing waters are designated as Site of Special Scientific Interest (SSSIs) in Britain and 32 have Area of Special Scientific Interest (ASSI) status in Northern Ireland. Some are designated as National Nature Reserves (NNRs). About 20 sites containing eutrophic standing waters are designated as Wetlands of International Importance under the Ramsar Convention. Most of these are also designated as Special Protection Areas (SPAs) under the EC Birds Directive. Six sites have been proposed by the UK as Special Areas of Conservation (SACs) under the EC Habitats Directive, for the category 'natural eutrophic lakes'. Under The Conservation (Natural Habitats) Regulations 1994, all public bodies and Government departments are required to ensure that the integrity of SACs is maintained. Whilst there are tight legislative controls over point source pollution, contamination from diffuse sources is much more difficult to regulate.