It lies in a hollow between Tarn Crag to the north and Blea Rigg to the south, about 910 feet or 280 metres above sea level.

The hollow was formed by a small corrie glacier, and is believed to have filled with water around 11,000 years ago when the ice finished melting.

Its outflow is Sourmilk Gill, named after the milky white colour of its waterfalls, which runs east towards Grasmere.

The gill displays impressive water scenery when seen from Grasmere, and from the path to the tarn.

The ascent was popular during the Victorian period, and a refreshment hut was even established in the 19th century by Robert Hayton of Grasmere above the outlet of the tarn to service the thirsty visitors.