vast water vast water
because it was carved out by glaciers which left tarns (or lakes)
There are 14 main bodies of water in the lake district but only one official "lake" and that is Bassenthwaite Lake. All the rest are "meres" or "waters", for example Windermere, and Coniston Water.
Lake Windermere
There is more than one lake in the Lake District, but the main one is Lake Windermere. It is 10.5 miles long, 1.25 miles wide and up to 220 feet deep.