(SFGate) - A state appeals court has restored the authority of California water regulators to direct reductions in cold-weather sprays by grape growers and other waterfront farmers along the Russian River that have led to deaths of endangered species of salmon.

A Mendocino County judge previously ruled that the state Water Resources Control Board lacked authority to restrict longtime users of river water. The First District Court of Appeal in San Francisco disagreed Monday, saying the board has the power to prohibit growers from "using water in an unreasonable manner" and to decide whether the protection of wildlife habitat outweighs growers' commercial needs.

The case dates from April 2008, when young salmon were found dead along the banks of the Russian River and its tributaries in Sonoma and Mendocino counties. The National Marine Fisheries Service estimated the deaths at 25,000 and said the main cause was sudden decreases in water levels because of spraying by farmers, mostly grape growers, to protect their crops from freezing during unseasonably cold weather.

Three years later, the state water board adopted regulations to reduce growers' use of river water in similar conditions. The board said it would allow designated groups of growers to propose detailed restrictions on water diversions, along with alternative crop-protection measures, subject to the board's approval.