Want to go on a day trip somewhere this weekend cos I have a car, which I usually don't, and weather is nice and friends are coming to visit and that. I'd like to go to near water, cos I used to live in Brighton and I really miss water, but don't want to drive to the coast cos that's quite far for a day. So ideally I'd like to visit somewhere pretty with a big lake in it or something, not too crowded or touristy, where we can take the dog and have a picnic and throw a frisbee and stuff like that.

Does anyone have any suggestions? I tried google but it's giving me a lot of standard touristy places. I'm in westish London if that makes a difference.