Blea Tarn is situated in a small hanging valley between Great Langdale and Little Langdale. The tarn itself was shaped by glacial ice moving over from nearby Great Langdale, but the ice was cut off as the glacier shrank, leaving "moraines very different from those at the head of the main valley".
Blea Tarn was designated a SSSI in 1989 because of its importance for palaeo-environmental studies relating to the Devensian and Flandrian times. Pollen analysis from Blea Tarn shows evidence for elm branches being collected as fodder from 3300 BC and forest clearances occurring from around 3000 to 2000 BC corresponding with the dates of the Great Langdale axe factory.
The nearby Side Pike SSSI was designated in 1977 as one of the few areas in the British Isles where rock demonstrating subaerial volcanic processes are seen. The ignimbrite and tuff rocks there form part of the Borrowdale Volcanic Group.
Blea Tarn Farmhouse
The farmhouse was built in the 17th century, with a later 19th-century addition, and is currently listed at Grade II. It is a National Trust property rented to a local family and is no longer a working farm. The farmhouse and tarn are both mentioned in Wordsworth's 'The Solitary':
"...to the south Was one small opening, where a heath-clad ridge Supplied a boundary less abrupt and close; A quiet treeless nook, with two green fields, A liquid pool that glittered in the sun, and one bare Dwelling; one Abode, no more ! It seemed the home of poverty and toil Though not of want: the little fields, made green By husbandry of many thrifty years, Paid cheerful tribute to the moorland House. ..."
— William Wordsworth, 1814
The tarn is easy to access with a National Trust a carpark across the road. Blea Tarn National Trust car park, grid ref: NY295043