Lake Mathews is a large reservoir located in Riverside County, California, in the foothills of the Temescal Mountains. Unfortunately, the lake is completely closed to public access, including all forms of paddling or recreational use. The reservoir is fully fenced and serves as the western terminus for the Colorado River Aqueduct, providing water for the Metropolitan Water District of Southern California.

The lake is surrounded by approximately 4,000 acres of protected land designated as the Lake Mathews Ecological Reserve. An additional 9,000 acres were added to create the Lake Mathews Estelle Mountain Reserve after the discovery of the endangered Stephens's kangaroo rat in the area.

While paddling is not permitted, the lake and surrounding area serve as an important bird habitat, particularly in winter months. Notable species include double-crested cormorants, western grebes, eared grebes, golden eagles, and bald eagles. The ecological reserve helps protect this important wildlife habitat.

Lake Mathews has a capacity of 182,000 acre-feet and is formed by an earthfill dam across the northern side of the basin. Two smaller dams, called dikes, were added in 1961 to increase the lake's capacity. La Sierra Avenue traverses the top of the west dike.

Despite its size and potential for recreation, Lake Mathews remains strictly off-limits to paddlers and the general public due to its critical role in Southern California's water supply infrastructure. Paddlers interested in flat water experiences in the region will need to seek out alternative locations that allow public access.