Blelham Tarn is a large valley tarn in the

Lake District The Lake District, also known as ''the Lakes'' or ''Lakeland'', is a mountainous region and National parks of the United Kingdom, national park in Cumbria, North West England. It is famous for its landscape, including its lakes, coast, and mou ...

of England, to the north of the hill Latterbarrow. The settlements of Outgate, Low Wray and High Wray are close by. The tarn is drained to the northeast by the short Blelham Beck into

Windermere Windermere (historically Winder Mere) is a ribbon lake in Cumbria, England, and part of the Lake District. It is the largest lake in England by length, area, and volume, but considerably smaller than the List of lakes and lochs of the United Ki ...

. This beck was previously straightened and lowered. Fish species in the tarn include

brown trout The brown trout (''Salmo trutta'') is a species of salmonid ray-finned fish and the most widely distributed species of the genus ''Salmo'', endemic to most of Europe, West Asia and parts of North Africa, and has been widely introduced globally ...

eel Eels are ray-finned fish belonging to the order Anguilliformes (), which consists of eight suborders, 20 families, 164 genera, and about 1000 species. Eels undergo considerable development from the early larval stage to the eventual adult stage ...

perch Perch is a common name for freshwater fish from the genus ''Perca'', which belongs to the family Percidae of the large order Perciformes. The name comes from , meaning the type species of this genus, the European perch (''P. fluviatilis'') ...

pike Pike, Pikes or The Pike may refer to: Fish * Blue pike or blue walleye, an extinct color morph of the yellow walleye ''Sander vitreus'' * Ctenoluciidae, the "pike characins", some species of which are commonly known as pikes * ''Esox'', genus of ...

and

roach Roach or The Roach may refer to: Animals * Cockroach, various insect species of the order Blattodea * Common roach (''Rutilus rutilus''), a fresh and brackish water fish of the family Cyprinidae ** ''Rutilus'' or roaches, a genus of fishes * Cal ...

,Blelham Tarn
/ref> much of the tarn shore is reedbed and waterfowl present can include

great crested grebe The great crested grebe (''Podiceps cristatus'') is a member of the grebe family of water birds. The bird is characterised by its distinctive appearance, featuring striking black, orange-brown, and white plumage, and elaborate courtship displa ...

whooper swan The whooper swan ( /ˈhuːpə(ɹ) swɒn/ "hooper swan"; ''Cygnus cygnus''), also known as the common swan, is a large northern hemisphere swan. It is the Eurasian counterpart of the North American trumpeter swan, and the type species for the genu ...

and golden-eye. The tarn is regularly monitored by the United Kingdom Lake Ecological Observatory Network and is characterised as

eutrophic Eutrophication is a general term describing a process in which nutrients accumulate in a body of water, resulting in an increased growth of organisms that may deplete the oxygen in the water; ie. the process of too many plants growing on the s ...

and

monomictic Monomictic lakes are holomictic lakes that mix from top to bottom during one mixing period each year. Monomictic lakes may be subdivided into cold and warm types. Cold monomictic lakes Cold monomictic lakes are lakes that are covered by ice throu ...

and has suffered from agricultural water pollution with large quantities of

blue-green algae Cyanobacteria ( ) are a group of autotrophic gram-negative bacteria that can obtain biological energy via oxygenic photosynthesis. The name "cyanobacteria" () refers to their bluish green (cyan) color, which forms the basis of cyanobacteria' ...

in the summer. The lake temperature at various depths varied over the period July 2012 to November 2014 between 2 and 25 Celsius as the air temperature (3 m above the surface) varied between -3 and 22 Celsius. Over the same period the pH varied from 6.4 to 9.8 and the dissolved oxygen ranged from 7 to 14 mg/L. Blelham Tarn and Bog, with a total area of 49 hectares, is designated a

site of special scientific interest A Site of Special Scientific Interest (SSSI) in Great Britain, or an Area of Special Scientific Interest (ASSI) in the Isle of Man and Northern Ireland, is a conservation designation denoting a protected area in the United Kingdom and Isle ...

SSSI units for Blelham Tarn & Bog
/ref> and Blelham Bog is designated a National Nature ReserveCumbria's National Nature Reserves
/ref> The bog contains various species of

sphagnum moss ''Sphagnum'' is a genus of approximately 380 accepted species of mosses, commonly known as sphagnum moss, also bog moss and quacker moss (although that term is also sometimes used for peat). Accumulations of ''Sphagnum'' can store water, since ...

bog myrtle ''Myrica gale'' is a species of flowering plant in the family Myricaceae native to parts of Eurasia and North America. Common names include bog-myrtle, sweet willow, Dutch myrtle, and sweetgale. Description ''Myrica gale'' is a deciduous shrub g ...

cotton-grass ''Eriophorum'' (cottongrass, cotton-grass or cottonsedge) is a genus of flowering plants in the family Cyperaceae, the sedge family. They are found in the cool temperate, alpine, and Arctic regions of the Northern Hemisphere, primarily in the mi ...

and the white-beaked sedge; and rare caddis-flies and vertigo lilljeborgi.

References

{{authority control Lakes of the Lake District National nature reserves in England Sites of Special Scientific Interest in Cumbria Westmorland and Furness Hawkshead