Lake Somerville State Park complex consists of four units: Birch Creek, Nails Creek, Lake Somerville Trailway, and the Somerville Wildlife Management Area. It is northwest of Brenham in Lee and Burleson counties. Birch Creek is 2,365 acres in Burleson County on the north shore, and Nails Creek consists of 3,155 acres in Lee County on the south shore near the west end of the reservoir. The two units are connected by a 13-mile trailway system. The Somerville Wildlife Management Area (WMA) consists of 3,180 acres with the Yegua Creek Compartment in southwest Burleson County and the Nails Creek Compartment in northeast Lee County.
The Somerville Reservoir was constructed by the U.S. Army Corps of Engineers. Work was started in June 1962, and deliberate impoundment of water was begun in January of 1967. The dam is located on Yegua Creek, 20 miles upstream from its confluence with the Brazos River, and about two miles south of Somerville. Somerville Reservoir covers 11,630 acres with a shoreline of 85 miles. Its main purposes are flood control, municipal water supply and recreation. The state park complex was leased from the federal government in 1969 and opened in 1970.
The Texas Parks and Wildlife Department manages the Somerville WMA under a license agreement and in cooperation with the U.S. Army Corps of Engineers.
Flag Pond is a 350-acre impoundment in the Yegua Creek watershed; it is located within the Lake Somerville State Park along the Somerville Trailway. The pond is a natural depression which has served as wetland habitat for waterfowl wintering (mid-October to mid-February) in the Lake Somerville vicinity. Flag Pond was originally developed by a private hunting club in 1926.