The longest rivers in the UK by country are:
England: River Thames (215 mi, 346 km)
Scotland: River Tay (117 mi, 188 km)
N. Ireland: River Bann (76 mi, 122 km)
Wales: River Tywi (64 mi, 103 km)
The largest lakes in the UK by country are:
N. Ireland: Lough Neagh (147.39 sq mi, 381.74 km²)
Scotland: Loch Lomond (27.46 sq mi, 71.12 km²)
England: Windermere (5.69 sq mi, 14.74 km²)
Wales: Llyn Tegid (Bala Lake) (1.87 sq mi, 4.84 km²)
The deepest lake in the UK is Loch Morar with a maximum depth of 309 metres (Loch Ness is second at 228 metres deep). The deepest lake in England is Wastwater which descends to 79 metres (258 feet).
As a result of its industrial history, the United Kingdom has an extensive system of canals, mostly built in the early years of the Industrial Revolution, before the rise of competition from the railways.
The United Kingdom also has numerous dams and reservoirs to store water for drinking and industry. The generation of hydroelectric power is rather limited, supplying less than 2% of British electricity mainly from the Scottish Highlands.