Interested parties appear likely to get the extra time many have requested to review and comment on some 3,600 pages of study for a plan to permanently reduce summertime flows in the Russian River and Dry Creek to benefit imperiled fish species.

Sonoma County officials announced Friday they would discuss an extension at the Oct. 4 Board of Supervisors meeting and may schedule additional public hearings on the flow rate in lower and upper river communities.

The plan has raised concerns among some business representatives and river residents about the reduced flows’ effects on recreation and water quality.

Board Chairman Efren Carrillo said Friday he’s “highly confident” fellow supervisors will agree to additional time for public feedback.

“We still need formal action,” Carrillo cautioned. “I don’t want to be presumptuous.”

The notice came three days after a standing-room-only crowd appeared before the Board of Supervisors to address a six-volume draft environmental impact report that envisions significant changes for how Russian River flows are managed by the Sonoma County Water Agency.

Many people complained before the board that the planned 60-day period of public review was woefully inadequate for anyone who wanted to have meaningful input. The comment period opened Aug. 19 and is scheduled to close Oct. 17. In addition, critics have said that a single public hearing in Santa Rosa, during normal work hours, no less, did not permit broad involvement.

“The Russian River is 110 miles long,” Supervisor James Gore said in a notice about the proposed extension, “and people raised concerns on Tuesday about the ability of folks throughout the watershed to participate in the process. By meeting in locations closer to their homes, we hope to get additional, productive input. This is a complicated issue and we understand why people want more time to review the document.”

For decades, releases from Lake Sonoma and Lake Mendocino have been used to raise stream flows during the dry summer months, when they would naturally be low.

But water managers are trying now to comply with a 2008 mandate from the National Marine Fisheries Service that requires lower in-stream flows to enhance rearing habitat for steelhead trout and coho salmon, both listed under the Endangered Species Act.

Under its existing state permit, the Water Agency has had to seek authorization to reduce stream flows each year, pending approval of a new management regime that is the subject of the current environmental review.

Under the proposed schedule, flows in the lower Russian River would drop between May and mid-October from 125 cubic feet per second to 70 cfs during normal rainfall years. In the upper river, north of Dry Creek near Healdsburg, minimum flows would fall from 185 cfs to 105 cfs.

The impact report found no significant harm to activities like swimming, sunbathing and boating. But it did suggest there could be an effect on water quality, capable of promoting nuisance algae, though that threat already exists.

Staff Writer Mary Callahan is at 521-5249 or mary.callahan@pressdemocrat.com.