Water Spider?

A great day today messing about in the pond, and a chance to try out my new waders ( a bargain from Lidels). The task was to clear some invasive rushes, during the process I saw this amazing spider, I've never seen one like it before, I rescued it from the water but it ran straight back in again and was quite at home walking on the surface of the water! Later I saw another one, must find out about them, any ideas? I have a friend over from Dorset, who was having fun taking photos of me, hip deep in water, managed not to fall in!