Coniston Water is a lake in the Lake District in North West England. It is the third largest by volume, after Windermere and Ullswater, and the fifth-largest by area. The lake has a length of , a maximum width of , and a maximum depth of . Its outflow is the River Crake, which drains into Morcambe Bay via the estuary of the River Leven. The lake is in the unitary authority of Westmorland and Furness, and the ceremonial county of Cumbria.
Coniston Water is situated within Furness, part of the North Lonsdale exclave of the historic county of Lancashire. It has been within the ceremonial county of Cumbria since 1974, and the Westmorland and Furness district since it replaced South Lakeland in 2023.
The lake is an example of a ribbon lake formed by glaciation. The lake sits in a deep U-shaped glaciated valley scoured by a glacier in the surrounding volcanic and limestone rocks during the last ice age.
To the north-west of the lake rises the Old Man of Coniston, the highest fell in the Coniston Fells group and the highest point in the historic county of Lancashire.
" 'The king's estate or village'. The second el.[ement] is OE tūn, and the whole name may, like numerous English Kingstons, be from OE 'cyninges-tūn'. ... Scand[inavian] influence is, meanwhile, shown by the '-o-' of early and modern spellings, and Ekwall speculated that this could have been the centre of a 'small Scandinavian mountain kingdom' ".
Plus "OE 'wæter', with the meaning probably influenced by its ON relative 'vatn'."
(OE=Old English; ON=Old Norse).
Remains of agricultural settlements from the Bronze Age have been found near the shores of Coniston Water. The Romans mined copper from the fells above the lake. A potash kiln and two iron bloomeries show that industrial activity continued in medieval times. In the 13th and 14th centuries, Coniston Water was an important source of fish for the monks of Furness Abbey who owned the lake and much of the surrounding land. Copper mining continued in the area until the 19th century.