Crummock Water lies north-west of Buttermere, separated from it by a ½ mile alluvial plain. At one time the two lakes were one, until the sediment build-up in the middle split them apart. This may have been exacerbated by the collapse of a moraine at the far end of what is now Crummock Water, lowering the water level of the lake(s).

The lake is bounded by Grasmoor to the north-east and Mellbreak to the south-west, both dramatic mountains. To the south there is a small sandy bay with a fence jutting into the water and partway along the lakeside road is Hause Point, which offers good views of both Mellbreak and Grasmoor.