Lime-Rich Natural Lakes
This habitat refers primarily to Malham Tarn. Lakes like this are extremely rare and unusual because limestone substrates are free draining. Malham Tarn is rich in calcium, but poor in other nutrients and is the highest marl lake in the UK.
It is particularly important for its submerged beds of stoneworts Chara spp alongside a range of Potamogeton species. The European crayfish occurs in the Tarn and associated upland streams.
