Boaters beware: Seasonal dam now up on Russian River

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A large rubber dam should be full Saturday on the Russian River near Forestville, creating a mandatory portage for summertime boaters as it helps deliver drinking water to 600,000 Sonoma and Marin county residents.

Warning buoys were placed across the river Monday morning at Sonoma Water’s massive concrete fish ladder just downstream from Wohler Bridge as technicians opened valves to let the submerged dam begin slowly filling with water.

By Friday, the bladder made of heavy duty rubber similar to a steel-belted vehicle tire was 99 percent full, said Barry Dugan, a spokesman for the county water agency.

The 11-foot high dam, reaching 175 feet across the river, will remain full all summer and into fall, with water spilling over the top and migrating fish getting around it via the $12 million fish ladder installed in 2016.

The facility features a video monitoring system enabling scientists to count fish and a viewing gallery that gives the public a glimpse as well, when open for tours.

The dam must fill slowly, Dugan said, to comply with regulations that prohibit the process from having a major impact on river flows above and below the dam.

All through summer, when water demand peaks, the dam creates a lagoon that Sonoma Water draws from to fill four off-stream infiltration ponds. Intentional seepage from the ponds recharges groundwater near three wells that pump water from about 80 feet below the stream bed.

The water, naturally filtered through sand and gravel, is so clean it needs no treatment, but chlorine is added as a precaution against possible contamination in the distribution system, the agency says.

Signs on both the Wohler Bridge and the buoys warn boaters of the change in conditions and the portage.

Once the dam is filled, the portage on the east side of the river is easily managed by boaters, Dugan said.

Recreation is prohibited on and near the dam and fishing is prohibited by the state Fish and Wildlife Department within 250 feet above and below the dam.

The dam is deflated in the winter when the river reaches a certain level and it lies on the river bottom to protect it from damage until spring.

You can reach Staff Writer Guy Kovner at 707-521-5457 or On Twitter @guykovner.

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