Lake Buchanan () was formed by the construction of Buchanan Dam by the Lower Colorado River Authority to provide a water supply for the region and to provide hydroelectric power. Buchanan Dam, a structure over 2 mi (3.2 km) in length, was completed in 1939. Lake Buchanan was the first of the Texas Highland Lakes to be formed, and with of surface water, it is also the largest. The surface of the lake includes area in both Burnet and Llano Counties. The lake is west of the city of Burnet, Texas.