The River Cober (Cornish: Dowr Kohar) is a short river in west Cornwall, England, United Kingdom. It rises in Nine Maidens Downs, directly between Hangman's Barrow to the west and the Nine Maidens stone circle to the east, in the former Kerrier District and runs to the west of the town of Helston before entering the largest natural lake in Cornwall – Loe Pool. The water is impounded by the natural barrier, Loe Bar, and the river system can be traced several kilometres out into Mount's Bay. Mining activity of over one hundred years in the river catchment, ceased in 1938, in the Wendron and Porkellis mining districts; and the engine house of Castle Wary (also known as Wheal Pool), near Nansloe can still be seen on the east side of the river below Helston. The lower reaches of river was canalised in 1946 and a causeway built over Loe Marsh in 1987. The meaning of the name is uncertain, but two of the earliest records are: "in 1260 we find, 'Chohor' and a few years later, 'Coffar'".