There are many more than one, it's just that only one has lake in it's name - Bassenthwaite Lake. Windermere, Coniston and Ullswater are all definitely lakes: http://en.wikipedia.org/wiki/Lake_District#Lakes
Windermere is a ****ing mere, you'll be surprised to know! Coniston Water and Ullswater are err waters!
Did you know that in a recent survey 2 out of 3 Rangers fans were found to be every bit as numb as the other one..