The tarn is drained to the northeast by the short Blelham Beck into Windermere.

[4] Fish species in the tarn include brown trout, eel, perch, pike and roach,[5] much of the tarn shore is reedbed and waterfowl present can include great crested grebe, whooper swan and golden-eye.

[6] The tarn is regularly monitored by the United Kingdom Lake Ecological Observatory Network and is characterised as eutrophic and monomictic[3] and has suffered from agricultural water pollution[7] with large quantities of blue-green algae in the summer.

[5] 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.