River Derwent and Bassenthwaite Lake

General site character

• Inland water bodies (Standing water, Running water) (96%)
  
• Bogs, Marshes, Water fringed vegetation, Fens (3%)
  
• Broad-leaved deciduous woodland (1%)
  

Annex I habitats that are a primary reason for selection of this site

• 3130 Oligotrophic to mesotrophic standing waters with vegetation of the Littorelletea uniflorae and/or of the Isoëto-Nanojuncetea

  Bassenthwaite Lake in the Lake District, north-west England, is an example of a mesotrophic waterbody (Type 5), an unusual type in mountain areas. It is a large lake with an extensive catchment area and consequently is subject to rapid through-flow of water and moderate nutrient status. A wide variety of pondweeds Potamogeton spp. are found, including perfoliate pondweed Potamogeton perfoliatus, small pondweed P. berchtoldii and curled pondweed P. crispus, which are widespread, whilst red pondweed P. alpinus, various-leaved pondweed P. gramineus and lesser pondweed P. pusillus are more locally distributed. Uncommon species present in the community are autumnal water-starwort Callitriche hermaphroditica and six-stamened waterwort Elatine hexandra. The shorelines are extensive and relatively undisturbed compared with other major Cumbrian lakes. Much of the shore is of shingle or gravel, but soft peat has accumulated around Bowness Bay. Several sedge species are found in such areas, including a local northern species, water sedge Carex aquatilis. On stony shores common spike-rush Eleocharis palustris is locally abundant amongst species such as globeflower Trollius europaeus, saw-wort Serratula tinctoria and the nationally rare thread rush Juncus filiformis. The lake also supports one of only two surviving UK populations of a rare fish, vendace Coregonus albula. Now extinct in Scotland, the only other known surviving population of vendace is found in Derwent Water, also in the Lake District.

Annex I habitats present as a qualifying feature, but not a primary reason for selection of this site

• 3260 Water courses of plain to montane levels with the Ranunculion fluitantis and Callitricho-Batrachion vegetation

Annex II species that are a primary reason for selection of this site

• 1065 Marsh fritillary butterfly Euphydryas (Eurodryas, Hypodryas) aurinia

  This site supports the largest area of appropriate habitat, M25 Molinia caerulea – Potentilla erecta mire, in Cumbria. The marsh fritillary Euphydryas aurinia population is spread over four habitat patches where numbers fluctuate annually but collectively form a moderate-sized and stable population.

• 1095 Sea lamprey Petromyzon marinus

  The Derwent represents sea lamprey Petromyzon marinus in a high-quality oligotrophic river in northern England. The extensive occurrence of gravels and silts in the middle to lower reaches of this river means that it is able to support a large population of sea lamprey.

• 1096 Brook lamprey Lampetra planeri

  The Derwent represents brook lamprey Lampetra planeri in a high-quality, oligotrophic river in northern England. Good populations of the species are known to occur, and this river has features that provide the necessary conditions for both spawning and nursery areas – extensive gravel shoals, good water quality and areas of marginal silt.

• 1099 River lamprey Lampetra fluviatilis

  The Derwent represents river lamprey Lampetra fluviatilis in an oligotrophic river in northern England. Good numbers of this species are known to occur and this river has features that provide the necessary conditions for both spawning and nursery areas – extensive gravel shoals, good water quality and areas of marginal silt.

• 1106 Atlantic salmon Salmo salar

  The Derwent represents Atlantic salmon Salmo salar populations in north-west England and is a particularly good example of a large oligotrophic river flowing over base-poor geology, providing a contrast to the more mesotrophic River Eden. Low intensity land-use in the catchment means there is good water quality throughout much of the system. This water quality, coupled with the presence of extensive gravel shoals, makes it a particularly suitable river for breeding and enables it to support a large population.

• 1355 Otter Lutra lutra

  The River Derwent and Bassenthwaite Lake represent good quality otter Lutra lutra habitat in north-west England. Together, the lake and river represent a wide range of suitable conditions for otters in a relatively upland environment.

• 1831 Floating water-plantain Luronium natans

  This site represents the northern limit of floating water-plantain Luronium natans in the UK, and its occurrence in relatively shallow, oligo-mesotrophic lakes. Within the site, the species is found in two lakes, Derwent Water and Bassenthwaite Lake. Both of these lakes have healthy populations of the species in extensive, species-rich beds of aquatic macrophytes. In Bassenthwaite Lake it also occurs on muddy lake-shores. These are the only two known sites for Luronium in the Lake District.

Annex II species present as a qualifying feature, but not a primary reason for site selection

• Not Applicable