DIVERSION LAKE. Diversion Lake, a reservoir on the Medina River, is four miles below Medina Lake and eleven miles north of Castroville in northeastern Medina County (at 29°31' N, 98°54' W). The dam was completed in 1913 at a cost of $288,000. The lake, owned and operated by Bexar-Medina-Atascosa Counties Water Improvement District No. 1, has a normal capacity of 4,500 acre-feet and a maximum capacity of 16,199 acre-feet. It is used mainly to divert water for irrigation. The reservoir was constructed to avoid the expensive and difficult engineering required to build an irrigation-canal system through the rugged canyons of the Medina River immediately south of Medina Lake dam. Water impounded by the upper dam is released into Diversion Lake, which covers about 400 acres. The Diversion Lake dam in turn controls the flow and amount of water released into an extensive irrigation system. The solid concrete dam, fifty feet high and forty-four feet wide at the base, is 440 feet long.
Castro Colonies Heritage Association, The History of Medina County, Texas (Dallas: National Share Graphics, 1983).