A short distance north of Malham, in Yorkshire, is Malham Tarn. A small lake with a surface area of 153 acres and a maximum depth of 14 feet, it is unusual for a number of reasons; as a result of which, it has been designated an SSSI (Site of Special Scientific Interest), NNR (National Nature Reserve) and SAC (Special Area of Conservation) as well as being listed as a RAMSCAR Site!
The Tarn is owned by the National Trust but, since 1947, has been leased to the Field Studies Council; the reason being that Malham Tarn and the associated wetlands have the greatest diversity of wildlife habitats of any upland lake in the UK.
In fact, at 377m above sea level, it is the highest lake in England.
Another feature which makes Malham Tarn unusual is that it has formed within an area of limestone, a permeable rock. The Tarn actually lies on a small bedrock of slate covered in marl; a calcium based mudstone which contains clay and silt. Because of this bedrock, the water of Malham Tarn has an alkaline pH; one of only eight of its kind in Europe!
The stream which flows out of the Tarn is only visible for about 500 metres, at which point it disappears, following underground channels through the limestone until it eventually emerges some 2 miles further downstream.
We weren't fortunate enough to spot a massive diversity of wildlife (though we did see a tree creeper), but we did have a close encounter with a small group of cows, including some calves, the mothers of whom were not too enthusiastic about our presence (on the footpath) in their field and approached us to do a bit of posturing to make their feelings clear.
After a bit of posturing of our own, they turned aside and we were able to back off and walk quietly on.
As you can see, it was a blustery day and walking by the edge of the water felt almost like being by the sea, the sound of the waves was so distinct :)