After heavy rains this week, dozens of coho salmon going up San Geronimo Creek found themselves stalled at a 10-foot high dam on golf course property near Nicasio Valley Road.
Many coho made it up the dam's fish ladder, but some jumped onto a lengthy concrete apron before the dam and thrashed about in shallow water until too exhausted to move.
"The problem at this dam is that the apron has collapsed from last years heavy rains, and the fish are having trouble finding the fish ladder," said Willis Evans of San Geronimo.
The fish ladder was built in 1954 with the help of Evans, who was then a fisheries biologist with the California Department of Fish and Game. The series of water-filled steps were designed for salmon to pass an old Roys Dam built long ago to protect agricultural lands, Evans explained.
However, now "the apron drops off in such a way [with a heavy flow area and scour-pool below] that it's like the fish get confused and jump on the apron, but they can't move [upstream] from there," said Bob Chamberlain of Lagunitas, a Trout Unlimited conservationist who has counted fish in San Geronimo Creek for 12 years.
"Certainly [the salmon] get beat up on that apron - they jump and land on concrete," said Gregory Andrew, a Marin Municipal Water District fishery biologist. "I wouldn't think they are getting killed right there, but they might give up and choose to go downstream and spawn there...
"If you have a big population crammed into a small area, one fish will spawn and another will come in and spawn over it, disrupting the original redd [spawning bed]," he continued.
To guide fish into the ladder, Andrew and Evans suggested the apron be lengthened to cover the broken concrete edge that draws fish, or that the entire dam be redesigned into one huge "fish ladder."
But, Evans noted, that won't help the fish get upstream this winter. He suggested people net the fish and carry them upstream or fence the creek to guide them toward the ladder flow.
California Department of Fish and Game, which issues permits for improvements for coho salmon habitat, had an investigator at the site late Wednesday afternoon, said Regional Manager Brian Hunter.
"At peak flows water is going to come over the dam no matter what you do," Hunter said.
Hunter said the landowner will be pressured to repair the area if there is a problem. Complicating matters, Hunter said, is the pending sale of the golf course to an out-of-state buyer. The new owners might end up paying for the work, or the bill might fall to the government, or a potential project could end up in court. The federal government also is soon to get involved, he said.
On Dec. 30, the coho will placed on the federal list of endangered species. "Because of the listing, we want to identify and fix all these problem areas in cooperation with all who are involved, such as property owners and California Fish and Game," said Jon Mann, an engineer with National Marine Fisheries Service - the agency that will soon oversee all coho habitat.
Mann said he plans to tour West Marin creeks next month.