Rushing to meet a Thursday deadline for detailing plans to preserve endangered fish, Sonoma County supervisors ordered reductions in flows along Dry Creek and the Russian River.

The instream flow reduction, regulated by water releases from dams upstream, won't take effect until next spring and will prompt an environmental impact study over the next two years.

The cutback is part of the county Water Agency's policy shift that abandons a long-standing request to increase water available to cities from 75,000 to 101,000 acre feet. That policy change is under discussion by county officials, who view it as inevitable, and by city officials, who want to ensure their residents don't lose water rights.

Supervisors also approved a $7.8 million line of credit with North Coast Bank, an amount that covers the estimated cost of coho-related preservation projects through 2013. Funding through joint projects conducted by the Water Agency and the state Department of Fish and Game will probably triple that cost through 2022, officials said.

"Having a cooperative agreement with the Department of Fish and Game is important in getting federal dollars," said board chairman Paul Kelley, who was in Washington last week discussing fish preservation with federal officials.

Pam Jeane, deputy operations director of the Sonoma County Water Agency, said an environmental study will "take at least a couple years." However, she said the National Marine Fisheries Service biological opinion concluded that fish habitat improvement could only occur if the velocity of water in the waterways was reduced.

"After filing our petition, the state will alert the public and anyone can file protests," Jeane said. "We are hoping that the state board will hold off so we can do the environmental review process."

Leaders of two environmental groups told supervisors that the review should be broad enough to address issues of long-standing concern about usage of water in Dry Creek and the Russian River.

Sierra Club representative Keith Kaulum said reports of "serious illegal diversion" by agricultural interests should be examined.

Brenda Adelman, of the Russian River Watershed Committee, said she worries that federal concern about low river flows upstream may inadvertently kill fish downstream where there might not be enough water for them to thrive. She said she fears that the federal biological opinion will reduce too much of the water flow along Dry Creek before it joins the Russian River.

"We have had low flows all summer. There is algae and ludwigia in the river," Adelman said. "In most places the water is ankle deep."