Castle Semple Loch is a 1.5-mile-long (2.5 km) inland freshwater loch at Lochwinnoch in Renfrewshire, Scotland. Originally part of an estate of the same name, it is now administered by Clyde Muirshiel Regional Park as a watersports centre. An RSPB bird sanctuary is located on the loch's southern shore.Loch historyEarly authors, such as Hector Boece (1465–1536), often use the term 'Garnoth' or 'Garnott' and may be referring to a single large loch incorporating Kilbirnie Loch and Loch Winnoch (Barr and Castle Semple Lochs). Boece in his book of 1527 the 'Historia Gentis Scotorum' (History of the Scottish People), says that this entity was nocht unlike the Loch Doune full of fische.There is a long history of drainage schemes and farming operations in the Lochwinnoch area, with co-ordinated attempts dating from about 1691 by Lord Sempill, followed by Colonel McDowal of Castle Sempil in 1774, James Adams of Burnfoot, and by others. Until these drainage works Loch Winnoch and Kilbirnie Loch nearly met and often did during flooding, to the extent that, as stated, early writers such as Boece, Hollings and Petruccio Ubaldini regarded the lochs as one, using the name 'Garnoth' or 'Garnott'.