Lake Mathews is a large reservoir in Riverside County, California, located in the Cajalco Canyon in the foothills of the Temescal Mountains.

Lawrence Holmes, Sr., who owned 1,100 acres in the future reservoir basin, lost his property to eminent domain in a lengthy court battle.

In the early 1990s, an additional 9,000 acres was added to the reserve after the discovery of the endangered Stephens's kangaroo rat (Dipodomys stephensi) in the area.

An out-of-court settlement was reached where MWD would monitor the quantity of water entering Lake Mathews from the creek and release 1.3 times that amount, minus dam seepage, into the Santa Ana River.

Mathews is of greatest importance as its outlet feeds directly into pipelines that connect to member water agencies serving 8.4 million people.

The scene from the 1953 movie Fair Wind to Java would have featured, among other things, a smoke-belching volcano constructed on one of the lake's islands.

[9] After their idea was rejected by the MWD board, the movie's producers reportedly constructed a lagoon and volcano on a studio backlot.

[11] California Assemblyman Kevin Jeffries, on February 14, 2012, introduced legislation, AB 1686, which would have opened the lake for limited recreation similar to that available at other MWD reservoirs or, at the very least, have allowed for low-impact hiking in the Ecological Reserve.