Authorities worried about rainwater building up behind a Riverside County (search) dam are evacuating more than 800 homes Friday morning.

A Corona Police spokesman said he believed there's a small leak in the Prado Dam (search), located about 50 miles east of Los Angeles. But a spokesman for the Army Corps of Engineers, which oversees the dam, said no leak was present.

Spokesman Fred-Otto Egeler said a crew is releasing water but it's being retained behind the dam.

Officers started evacuating about 330 mobile homes and 508 other homes at 1 a.m. PST.