The River Irt is a river in the county of Cumbria in northern England. It flows for 14 miles (22 km) from the south-western end of Wast Water, the deepest lake in England, leaving the lake at the foot of Whin Rigg, the southern peak of the famous Wastwater Screes. The name of the river is believed to derive either from the Old English gyr which means "mud", or from the Brittonic words *ar, "flowing", or *īr, "fresh, clean, pure", suffixed with -ed, a nominal suffix meaning "having the quality of...".