An environmental group has mounted a new legal challenge over an endangered fish that could once again slow the massive Northern California water pumps that deliver two-thirds of Southern California's water.

The latest legal challenge, which comes just as the state started to ramp the pumping stations back up after a May 31 shutdown, could hurt all Californians, because regional water officials have already started dipping into backup water storage.

Any lengthy slowdown of the pumps would mean taking more water out of storage, which, if combined with another dry year in California, could lead to mandatory water cuts for some farmers.

Officials from the Natural Resources Defense Council said Wednesday that they have petitioned U.S. District Court Judge Oliver Wanger to issue a temporary restraining order that could slow the massive State Water Project pumps back to a trickle in order to protect an endangered fish, the delta smelt. Wanger is scheduled to hear the petition Friday.

Water officials around the state, meanwhile, said they were stunned when the state abruptly shut down the pumps May 31 because they were killing delta smelt, the two- to three-inch fish that lives only in Northern California's Sacramento-San Joaquin bay delta. The delta is the fragile heart of California's State Water Project.

Regional and local officials had mixed reactions Wednesday to the news of the latest attempt to slow down the pumps.

Officials from Southern California's main water supplier, the Los Angeles-based Metropolitan Water District, said again that any lengthy shutdown or slowdown of the State Water Project pumps would hurt regional supplies. But 18-month backup supplies were nearly full, officials said, adding that they would wait until Friday's potential ruling to comment further.

San Diego County agriculture officials said Wednesday that there was a growing sense of resignation among local fruit tree and avocado growers, who would be the first to suffer mandatory water cuts if they were ordered this summer or in 2008.

Some growers, particularly San Diego County's $300 million avocado and citrus industry, buy "interruptible" agriculture water at much cheaper rates, with the condition that they would take 30 percent cuts before anyone else if water rationing became necessary.

Eric Larson, executive director of the San Diego County Farm Bureau, said local agriculture officials on Tuesday night got word of the latest legal challenge and possible pump slowdown.

Although there has been no mention of any mandatory water cuts by Metropolitan, Larson said that tree growers - citrus and avocado - were wary.

The bay delta's legal and regulatory problems have only worsened a bleak California water picture. Southern California is in the midst of a severe single-year drought. The Colorado River - which, along with the State Water Project, is Southern California's main source of imported water - is in its eighth year of drought. And, before the pump shutdown, the State Water Project had suffered a bleak winter snow pack that cut supplies to 60 percent.

Larson said even if the latest challenge doesn't push the system to the brink, growers feel that another dry year in Northern California could do it in 2008.

He said most growers would probably deal with any water cuts by taking 30 percent of their trees out of production, rather than by trying to stretch 30 percent less water over 100 percent of their groves.

"There's a mood of resignation," Larson said. "Imagine if your boss walks in and says your income is going to be slashed by 30 percent, but your house payment is going to stay the same, and your car payment is going to stay the same."

Kate Poole, an attorney for the Natural Resources Defense Council, said Wednesday that the group filed its lawsuit to slow down the bay-delta pumps because state operators - in their desire to ramp the pumps back up and jump-start water deliveries - have ignored biologists' recommendations to slow down because smelt were still being killed.

State officials shut down the pumps May 31, hoping the endangered fish would migrate away from the pumps to another portion of the bay delta.

The state restarted limited pumping June 10 and have slowly ramped back up to near-normal speed.

Metropolitan General Manager Jeff Kightlinger said when the pumps were shut down last month that Metropolitan had enough stored water to last the region 18 months or so. Metropolitan delivers water to nearly 18 million Southern Californians in six counties, including San Diego.

But Kightlinger also said that if the shutdown lasted longer than 10 to 12 days, Southern California could lose some of its summer water allotment because there would not be enough days left in the year left to deliver the entire supply. And, he said, if the shutdown lasted a month, Metropolitan could look at cutting water supplies - starting with growers.

Congress members from California are pushing for governmental solutions to the delta pumping problems.

U.S. Rep. Brian Bilbray, R-Solana Beach - who signed a congressional delegation letter last week urging Gov. Arnold Schwarzenegger and federal officials to restart the bay-delta pumps - said the new potential slowdown should cause a cry for change.

Schwarzenegger and state legislators have started lobbying to resurrect the idea of a peripheral canal that was rejected by Northern California voters in the 1980s.

"This is exactly why so many of us were saying the peripheral canal was the way to go in 1982," Bilbray said. "We're talking about 50 percent of our water in San Diego. This is no little issue."

The canal would be built around the fragile bay delta to continue delivering Northern California rainfall and snow melt to Southern California, without damaging the bay delta or its inhabitants.

- Contact staff writer Gig Conaughton at (760) 739-6696 or gconaughton@nctimes.com.