An appellate court has upheld state rules regulating how hundreds of farmers in Sonoma and Mendocino counties divert water from the Russian River to ward off frost.

The rules, aimed at protecting fish, were struck down in 2012 by Mendocino County Superior Court Judge Ann Moorman, who declared the law to be "constitutionally void" and "invalid."

The state's First Appellate District court reversed her decision in a ruling filed Monday.

The State Water Resources Control Board lauded the decision.

"The board is pleased with the court's unanimous decision upholding the Russian River frost protection regulations," Michael Lauffer, the board's chief counsel said in a statement.

Mendocino County Farm Bureau Manager Devon Jones said the appellate court ruling is a disappointment.

"We felt there was a very good opinion," she said of the overturned ruling.

State regulators created the rules to prevent endangered and threatened salmon and steelhead trout from becoming stranded and dying when farmers pump water from the Russian River to ward off frost. Water is sprayed on vines to create a protective ice shield when temperatures fall below freezing.

The goal of the state rules is to avoid the sudden drops in river flows that can be caused when farmers throughout the river system pump water at the same time.

Several incidents in which rapid declines in river flows caused fish to become stranded triggered the regulations. Fisheries officials estimated some 25,000 salmonids were killed in two April 2008 episodes, one each in Sonoma and Mendocino counties. The incidents coincided with freezing temperatures, state officials said.

National Marine Fisheries Service officials blamed the strandings largely on farmers, especially grape growers. Grape plants are particularly susceptible to frost damage when new growth appears in the spring, the appellate court ruling noted. The Russian River watershed is home to more than 60,000 acres of vineyards. Of those, 70 percent are within 300 feet of salmonid habitat, the ruling said.

Following the 2008 strandings, federal fisheries officials urged the water board to regulate water diversions for frost protection. A task force was created and public hearings were held before the state water board adopted rules in September 2011. Rather than setting water diversions, the water board rules required that local agriculture groups be formed to study water flows and develop plans for managing their water diversions for frost protection. It included requiring that farmers install stream flow gauges and measure and report how much water is diverted for frost protection. Their plans would be subject to approval by the state water board.

But farmers, led by Redwood Valley grape grower Rudy Light, sued the Water Resources Control Board. The lawsuit alleged the science behind the regulations was vague; the state hadn't proved they are necessary; and that the water board overstepped its authority.

Moorman ruled in their favor in 2012, rejecting the state's frost protection rules. She said the board infringed on water rights and wrongly required farmers to gather information and create regulations themselves at great expense. She also said it appeared several factors, not just frost protection, contributed to the fish deaths.

Moorman additionally said the regulations were too sweeping and warned of economic devastation. She said the state's environmental impact report on the rules was inadequate because it did not sufficiently consider the impacts the rules could have on the economy, she said.

The appellate court disagreed with Moorman's conclusions, upholding the state's authority to implement the rules and its impact report.

Jones said affected farmers are still studying the new ruling and that she does not know whether an appeal is planned.

Nick Jacobs, attorney for the Sonoma County farmers, Russian River Water Users for the Environment, said he is still evaluating the ruling and does not yet know whether his clients will appeal.

But he was critical of the ruling.

"The trial court judge found the regulation and supporting environmental impact report to be invalid for eight separate reasons — it is hard to understand how less than two years later a different panel of judges can come to the opposite conclusion on each of the eight reasons," he said.

Jacobs also said the same appellate court 40 years ago came to a different conclusion in a similar case in Napa County.

"It is difficult for lawyers and clients to assess the state of the law when Courts of Appeal change the law after four decades."

Light and his attorneys could not be reached Tuesday for comment.

State water officials said many wine grape growers already have begun coordinating their frost protection diversions and taking other steps to avoid harming fish.

"When the (court) decision is final and the regulations restored, the board anticipates a Russian River-wide system of plans that will afford protections to endangered species while continuing to allow growers to protect wine grape crops from frost in a coordinated manner," Lauffer said.

You can reach Staff Writer Glenda Anderson at 462-6473 or glenda.anderson@pressdemocrat.com.