Salmon in San Lorenzo Creek

San Lorenzo Creek flows through a concrete channel for the first five miles upstream from the Bay. Fish can rest in pools along it, but cannot reach the natural streambed they need to spawn.

photos by Bruce King

Salmon have been spotted swimming up San Lorenzo Creek from the Bay to spawn but are being stopped by barriers installed in the 1960s meant to control flooding. 

Chinook salmon recently spotted swimming upstream in San Lorenzo Creek.

“We have a fall run of Chinook salmon migrating up San Lorenzo Creek. This is a very big deal!” Bruce King, president of Friends of San Lorenzo Creek, wrote in an e-mail.

“A few citizens spotted some big fish following the Oct 24 atmospheric-river storm and subsequent high creek flows. Friends of San Lorenzo Creek then documented this run of salmon along all five miles of the engineered (concrete) channel from the Bay to downtown Hayward. On Nov. 6, we found 28 salmon, 23 live and five dead, dispersed throughout the entire channel.”

He added that the fish are from 18 to 31 inches in length and that the run is continuing.

The creeks group has kept the Alameda County Flood Control & Water Conservation District informed of the run, King said. That agency built the channel and is charged both with flood prevention and keeping the county’s creeks healthy.

Reports of migrating salmon or trout had been infrequent since the channel was completed in the early 1960s, King said. Typically, only an individual fish would be spotted.

He said when fish try to swim upstream to spawn, the first barrier to their passage is a velocity ramp in the channel just before Foothill Boulevard in Hayward. Chinook salmon migrate upstream only once to spawn, stop feeding once they enter freshwater, and then die after spawning. 

“So, the salmon we are observing are not making it past the fish barrier and are dying in the engineered channel,” King said.

The creek group is calling for removing barriers, perhaps building a fish ladder, along San Lorenzo Creek so the fish will be able to swim far enough upstream to spawn. They’d also like to see resting pools along the way so the fish will be able to complete the journey. 

A little further south, the Alameda County Flood Control is joining with other agencies to build such a fish ladder on Alameda Creek, which runs through the Fremont area. That ladder, to help fish get past a barrier protecting BART and Union Pacific tracks from erosion, is scheduled to open by the end of this year.

A study for the district in 2006 called for building fish ladders on creeks where barriers block natural fish migrations, but the only such project underway is the one on Alameda Creek. King said he hopes evidence of a natural migration on San Lorenzo Creek may prove important to removing barriers there as well.