Loch Rannoch (lŏkh răn´əkh), lake, 91/2 mi (15.3 km) long and 1 mi (1.6 km) wide, Perth and Kinross, central Scotland, in the Grampians. It is fed by the Ericht River and drained by the Tummel River to the Tay River. Part of a hydroelectric project, a power station was constructed at the west end. The lake is known for trout and salmon fishing. The Black Wood, a remnant of the ancient Caledonian forest, is on the southern shore.