The Ayrshire/Lanarkshire border runs north to south across the Loch. The "Loch" is in fact a dam created in 1802 by James Finlay for his Catrine cotton works.
The boundary between Ayrshire and Lanarkshire follows a path that runs from north to south along the dam built in 1802 by James Finlay at his Catrine cotton mill. The "Loch" is the name given to this structure.