This is Wet Sleddale dam. Every year in wet periods water pours over the top of the dam wall and creates wonderful patterns when the wind blows, which it was today. The dam was completed in 1966. It holds 2,300 million litres of water, is 21m high and 600m long. The water is carried from this reservoir to Haweswater reservoir mainly through tunnels. From there water is supplied to a large area of the North West England, including Manchester.
I had another shot of the dam from further off earlier in the year. Here is the link. http://365project.org/shirleybankfarm/365/2015-12-16
Also if you look at this picture I posted in December you can just make out the dam in the distance, without water pouring over it. http://365project.org/shirleybankfarm/365/2016-01-20
