Lakes & Reservoirs (definition)

Durham Lowland Priority Habitats
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Lakes and Reservoirs Habitat Definition

This habitat definition includes standing open waters over 2ha in size. This includes natural lake systems as well as man-made waters such as reservoirs and flooded gravel pits. Standing open waters perform an important function in their ecosystems, storing water and reducing flood risk and achieving important water quality improvements prior to the water reaching a stream or river.

There are three main types of standing waters: oligotrophic (nutrient-poor), eutrophic (nutrient-rich) and mesotrophic (intermediate). For the purposes of the Durham BAP, only eutrophic and mesotrophic standing waters are included.

Identification and mapping

For the purposes of mapping, this definition covers the open water zone, which may contain submerged, free floating or floating-leaved vegetation, and also water fringe vegetation and adjacent land up to the winter high water mark. Adjacent habitats that come within the high water mark and meet other BAP habitat definitions (such as lowland fen, reedbed or wet woodland) should be additionally recorded and mapped as those habitats.


Eutrophic standing waters are nutrient rich, either naturally or as a result of artificial enrichment. They are highly productive and can sustain large populations of fish and waterfowl. They are characterised by having dense, long-term populations or algae in mid-summer, often making the water green. Their beds are covered by dark anaerobic mud, rich in organic matter. They will be typically found along coastal areas.

Eutrophic standing waters are an important habitat for a number of priority species. Bottom-dwelling invertebrates such as snails, dragonflies and water beetles are abundant and calcareous sites can support populations of white-clawed crayfish. Amphibians including great crested newts are often present and the abundance of food can support internationally important bird populations.


These are bodies of standing water characterised by having a narrow range of nutrients, the main indicatives ones being inorganic nitrogen (N) and total phosphorus (P) and are in the middle of the trophic range (with a pH usually around or slightly below neutral). They are largely confined to the margins of upland areas.

Relative to other standing waters they contain a higher proportion of nationally scarce and rare aquatic plants. They are also important for dragonflies, water beetles, stoneflies and mayflies. In general, fish communities in mesotrophic standing waters are a mix of coarse and salmonid species.