Castle Loch, Port WilliamCastle Loch is a large, shallow, freshwater loch in Dumfries and Galloway, in the Southern Uplands of south-west Scotland. It lies to the west of Mochrum Loch and about west of the town of Wigtown. The loch has 2 islets.SurveyThe loch was surveyed in 1903 by James Murray and later charted as part of Sir John Murray's Bathymetrical Survey of Fresh-Water Lochs of Scotland 1897-1909.