The tarn is one of the sites in DEFRA's UK Upland Waters Monitoring Network. It occupies and lies at an altitude of in a moraine hollow on the uplands between Wastwater and Eskdale. The lake has two distinct basins close to the south-eastern shore and a maximum depth of . There are four main inflow streams to the north and north-west. The outflow at the eastern end joins the Hardrigg Beck which drains the slopes of Scafell and, in times of especially high flow, is partly diverted into the lake across a braided delta.