The Ross Barnett Reservoir, often called the Rez, is a reservoir of the Pearl River between Madison and Rankin counties in the U.S. state of Mississippi. The 33,000-acre (130 km2) lake serves as the state's largest drinking water resource, and is managed by the Pearl River Valley Water Supply District. The lake features 105 miles (169 km) of shoreline impounded on the south by a 3.5-mile (5.6 km) man-made dam and spillway. The western shore is bounded by the historic Natchez Trace Parkway.