A National Academy of Sciences panel has concluded that the much-disputed fish protections that have curbed water deliveries to the San Joaquin Valley and Southern California are scientifically justified.
The findings, contained in a report that will be released Friday, largely validate environmental actions taken by two federal agencies to save the imperiled delta smelt and protect declining populations of salmon that migrate through the Sacramento-San Joaquin delta.
The protections, imposed under the federal Endangered Species Act, have recently grown stricter, compounding water shortages stemming from the state's three-year drought.
Central Valley farm interests, some politicians and the Metropolitan Water District of Southern California, which imports water from the delta, have sharply criticized the curbs as overly strict and unfounded.
But in its 64-page report, a committee of more than a dozen experts from around the U.S. found otherwise.
The panel acknowledged that the pumps that draw huge amounts of water from the delta and send it south are not the only factors hurting the delta environment. They called for more monitoring and studies and emphasized that "reversing or even slowing the declines of the listed species cannot be accomplished immediately."
The committee also conceded that there was "substantial uncertainty" about where to set a key trigger for the pumping limits, which change according to delta flows, the location of the fish and other conditions.
But the experts repeatedly said that despite such reservations, the federal actions were "scientifically justified."
The evaluation was undertaken at the behest of the U.S. departments of Interior and Commerce after Sen. Dianne Feinstein (D-California) asked the agencies to launch an academy review of the protections.
The report, a copy of which was obtained by The Times, is the first part of a two-year review by the National Research Council, an arm of the National Academy of Sciences.
The group considered a number of alternative actions that could have less of an effect on water exports -- such as reducing delta contaminants or predation by nonnative species.
The report said none of those actions "had received sufficient documentation or evaluation to be confident" that they would provide equal or greater protection for smelt and salmon.
The panel also rebuffed arguments that the environmental limits have failed to halt the delta smelt's precipitous decline. "It is unrealistic to expect immediate and proportional responses to actions . . . especially within the first few years of implementation," the scientists wrote.