The 5,500 ha (14,000 acres) island, mostly managed by Reclamation District 341,[2] is the meeting point of Sacramento, Solano, and Contra Costa Counties, and is bordered on the north and northwest by the Sacramento River, on the northeast by Three Mile Slough, and on the east, and south west by the San Joaquin River.

[4] Currently, it is 10 feet below sea level, due to the drainage of wetlands in the Delta which has dried out its peat soils, resulting in land subsidence.

In either case, turn south onto Sherman Island Road and continue driving to Mayberry Slough.

[6] The southwest of the island, known as Lower Sherman Island Wildlife Area, contains about 3,100 acres (1,300 ha) and features a large marshy area and Sherman Lake where there is fish[a] and other water sports, particularly windsurfing and kiteboarding.

Senate Bill 1065, enacted in 1991, was intended to assure that these islands did not experience any net loss of habitat.