A federal judge has ruled that California's water systems threaten to push native salmon into extinction, but stopped short of ordering any immediate water cutbacks farmers said could cost millions in lost crops.

The ruling in a Fresno federal court Friday ultimately could force regulators to change the way they move and use water to prioritize letting the endangered fish breed in the state's rivers and migrate into the Pacific Ocean.

U.S. District Judge Oliver Wanger denied environmentalists' and fishermen's requests to order more water to be stored in a federal reservoir in an effort to protect the habitat of the dwindling winter- and spring-run salmon and native steelhead populations.