Malham Tarn

Malham Tarn lies in the Yorkshire Dales, a national park of rolling limestone hills and open moorland. The lake sits 377 metres above sea level, making it the highest marl lake in Britain. It is one of only eight upland alkaline lakes in Europe, with water that stays between pH 8.0 and 8.6. The catchment covers 600 hectares, and the lake is fed by a stream at its north-west corner. Water takes about eleven weeks to travel through the basin before emerging near Malham Cove as part of the River Aire. The site has long been recognised for its wildlife. Six kinds of fish live in the lake, along with white-clawed crayfish and several rare water beetles. Moorhens, tufted ducks and teal glide across the surface while curlews and lapwings nest on the surrounding moor. Two copepods found here, Bryocamptus rhaeticus and Moraria mrazeki, grow no higher in Britain. Wild cranberry and bearberry grow on the shores, and purple moor grass sways in the wind. Visitors walk a clear path around the 62-hectare water. The lake’s southern end holds a sluice gate added in 1791 that still controls the level. On the northern shore stands Malham Tarn House, once a hunting lodge and later a field centre. The house and its stone buildings now serve the National Trust’s rangers and landscape teams. Beyond the water, the moor stretches to Malham Cove, where the outflow disappears underground before reappearing downstream.