CALIFORNIA -- An "unprecedented" environmental ruling issued late Friday by a federal court judge could create Southern California's worst water shortages since the state's last widespread drought more than 15 years ago, water officials said.

Officials from around the state said on a teleconference call Friday that they were still trying to decipher the ruling from U.S. District Court Judge Oliver Wanger that would curtail pumping water through the fragile Sacramento-San Joaquin bay delta to save an endangered fish, the delta smelt.

But they said the decision could cut life-sustaining water supplies from the north to Central and Southern California by 14 percent to 35 percent, a ruling that Gov. Arnold Schwarzenegger immediately called a "devastating blow to our water supply system and the state economy."

Officials from the Los Angeles-based Metropolitan Water District, Southern California's main water supplier, said the region, including San Diego County, could lose up to 30 percent of the Northern California water -- water that made up two-thirds of the region's total supplies this year.

However, Metropolitan officials, who are in the process of creating a plan to divvy water supplies in a shortage, said it was too soon to say they would issue mandatory water cuts next year that could trickle down to the public.

"We're not predicting any type of rationing, but it's a significant hit," Metropolitan General Manager Jeff Kightlinger said. "But it's going to definitely cause pain."

Wanger's ruling would curtail pumping starting Christmas Day, around the weeks when smelt are about to spawn, until June, when young fish can move into areas away from the bay delta's pumps.

Dennis Cushman, assistant general manager of the San Diego County Water Authority, said Wanger's decision was "very complicated," because it sewed together pieces of several proposals to cut bay delta pumping. The proposals were forwarded to Wanger by water agencies, state and federal officials and environmentalists who sued to save the smelt.

In a suit earlier this year, environmentalists asked the courts to shut down the pumps in California's State Water Project and the federally run Central Valley Project because they were sucking in and killing smelt in the bay delta.

The State Water Project, a 600-mile-long stretch of dams, reservoirs and pipelines, brings water to Southern California. The bay delta is the heart of the project. The Central Valley Project delivers water to people and farms in central California.

Between the two, the projects serve more than 25 million people and thousands of acres of crops.

Both environmentalists and water officials agree that the smelt population has declined precipitously. The fish are protected under the California Endangered Species Act, and their well-being is considered a measure of the environmental health of the fragile bay delta ecosystem.

Environmental groups proposed Wanger cut the pumping times by 54 percent. Water agencies offered a plan that would cut the pumps by just 7 percent. State and federal officials proposed a cut of up to 34 percent.

Southern California also gets imported water from the Colorado River but has relied more heavily on the State Water Project since 2003, when it signed a deal with other Western states to stop "overusing" the river.

Wanger said Friday that pressure from the pumps helped reverse the natural direction of water within the bay delta, damaging habitat and the smelt, which experts say might be on the brink of extinction.

State and federal officials argued that other factors led to the fish's decline.

But Wanger said there was "uncontradicted evidence" that the pumps were contributing to killing the fish.

"It happens, and the law says something has to be done about it," Wanger said.

Environmentalists largely welcomed Wanger's decision as an improvement over current conditions.

"It's better than what there was before," said Trent Orr, an attorney with the environmental group Earthjustice, which was party to the suit.

But environmentalists wanted more, said Orr, including measures that would have protected habitat from encroaching salt from the San Francisco Bay in the fall.

Cushman, meanwhile, and other water officials said people around the state should ratchet up their efforts to cut back water use now if they haven't already, in order to keep water stored in reservoirs.

"If we conserve in 2007, there may be additional water we can use next year," he said. "We (Water Authority) are challenging every person to conserve 20 gallons of water per day."

Associated Press reports contributed to this article. Contact staff writer Gig Conaughton at (760) 739-6696 or gconaughton@nctimes.com.