Malham Tarn
Malham Tarn is an extraordinary natural feature of the Yorkshire Dales, the highest natural lake in England, lying at over 380 metres above sea level in a limestone landscape of exceptional geological interest. The tarn and its surrounding environment form a National Nature Reserve and a Site of Special Scientific Interest, protected for both its ecology and its unusual geological situation. What makes Malham Tarn particularly unusual is its very existence. Limestone is a porous rock through which water typically drains quickly rather than forming permanent lakes. The tarn exists because it sits above an impermeable layer of Silurian slate at the bottom of a glacially scoured basin, trapped by a geological fault that juxtaposes the permeable limestone with rock that holds water. The surrounding limestone landscape drained rapidly after the last Ice Age, leaving behind a patchwork of dry valleys, limestone pavements and springs that makes the Malham area one of the finest karst landscapes in Britain. The tarn and surrounding fen, marsh and calcareous grassland support an outstanding range of wildlife. The fen community in particular contains plant species associated with the high calcium levels produced by the limestone bedrock, including rare sedge communities and wetland plants that have become scarce across much of northern England. The tarn itself supports breeding populations of several water birds and is an important feeding site for migratory species. The field study centre on the tarn shore, established in 1947, has been a base for ecological research and environmental education for more than 70 years. The landscape around Malham Tarn can be explored as part of the Malham circular walk, one of the most popular and rewarding day walks in the Yorkshire Dales. The full circuit takes in not only the tarn but also the spectacular Malham Cove, a curving limestone cliff 80 metres high with an extensive limestone pavement at its summit, and Gordale Scar, a dramatic limestone gorge with two waterfalls that can be climbed with care in dry conditions. The combination of dramatic geology, clear walking paths and the varied scenery between these features makes the Malham area one of the best day walking destinations in northern England.