Kilbirnie Loch is a freshwater Loch situated in the floodplain between Kilbirnie, Glengarnock and Beith, North Ayrshire, Scotland. It runs south-west to north-east for almost 2 km (1.2 mi), is about 0.5 km (0.31 mi) wide for the most part and has an area of roughly 3 km2. It has a general depth of around 5.2 metres to a maximum of around 11 metres. The loch is fed mainly by the Maich Water, which rises in the Kilbirnie Hills near Misty Law, and is drained by the Dubbs Water that runs past the Barr Loch into Castle Semple Loch, followed by the Black Cart, the White Cart at Renfrew and finally the River Clyde. The boundary between East Renfrewshire and North Ayrshire, in the vicinity of the loch, runs down the course of the Maich Water along the northern loch shore to then run up beside the Dubbs Water.