The lake's primary inflow is Buttermere Dubs, itself the outflow of Buttermere, and its outflow is the River Cocker, which meets the River Derwent at Cockermouth before entering the Irish Sea at Workington.

The hill of Mellbreak runs the full length of the lake on its western side; as Alfred Wainwright described it 'no pairing of hill and lake in Lakeland have a closer partnership than these'.

[2] Water from the lake was treated at Cornhow water treatment works, near Loweswater,[3] and was distributed to the towns of Silloth-on-Solway, Maryport, Workington, and many smaller towns, villages, and hamlets in the surrounding area for drinking and all other uses.

[4] This use ceased in October 2022 with the commissioning of the United Utilities pipeline to bring supply from Thirlmere.

[5] Crummock Water gained attention in 1988 when the body of Sheena Owlett was found in the lake.