The lake runs through classic East Texas Piney Woods forests. Water quality is generally good, with an average depth of 20.5 feet (6.2 m), and a maximum depth of 75 feet (23 m). The controlling authority of the lake is the San Jacinto River Authority. The City of Houston owns a two-thirds interest in the lake; the SJRA owns one-third. The lake extends about 21 miles (34 km) in length and covers 20,118 acres (81.41 km2) with 5,000 acres (20 km2) in Sam Houston National Forest and capacity of 430,260 acre feet (530,720,000 m3). Lake Conroe was conceived in 1970 as an alternate water supply for the city of Houston. The lake was completed in January 1973, and it was filled on October 31, 1973.