Winter Run - 2016 Fish Die Off

The Setting

Pescadero Creek forms a coastal watershed in San Mateo County, located about 50 miles south of San Francisco. The watershed supports a large bar built estuary, or lagoon, and a marsh complex in the lower watershed. The lagoon fills with freshwater when a sandbar forms at the creek mouth. Once the sandbar is formed, high tide events bring salt water into the lagoon, either through the sandbar or over the top as waves wash in. Lagoons are highly productive habitat for migrating and young steelhead. As juveniles, steelhead rear in lagoons and grow quickly to a large size. In essence, Pescadero Lagoon serves as a nursery for steelhead to develop before entering the ocean.

Hundreds of steelhead, protected under the Endangered Species Act, have died off in Pescadero Lagoon again in 2016. The California Department of Fish and Wildlife counted 435 dead fish and observed 500 to 1,000 more that were swimming lethargically and likely to perish. The latest fish kill occurred early November 2016 after rain the previous night caused the swelling lagoon to break through the sandbar at Pescadero State Beach, sucking water out of Pescadero Marsh Natural Preserve and into the ocean. Roughly 2,000 fish — including steelhead, flounder and sculpin — asphyxiated in oxygen-depleted water, according to Steve Simms, who has tracked the problems in the marsh for more than a decade.

“I’m just totally frustrated,” said Simms. “It’s hard to deal with and hard to understand how we can still be at this point after so many years.” However, Simms said he is encouraged that State Parks — along with state and federal wildlife agencies — is now considering a proposal to dredge part of the marsh to improve fish habitat.

State Parks has long resisted fixing the strange hydrologic conditions in the marsh, which is fed by Pescadero and Butano creeks, insisting that the matter requires further study. The agency convened a volunteer science panel in 2013 to assess the marsh and make recommendations. The panel delivered its report this past March, more than two years late, and declined to lay out a specific plan of action.

Pescadero Marsh South of lagoon and near mouth of Butano Creek

State Parks is now exploring one option provided by the science panel: unclogging the lower end of Butano Creek, which is choked by sediment and marsh vegetation. Removing tule reeds and dredging of the thalweg of Butano Creek opens fish passage as well as flushes organic-rich sediment from the system during strong winter flows. Improving the creek's channel will increase tidal flushing in this part of the lagoon. But, while dredging will open the channel, the lagoon still receives excess sediment and the channel will fill again. Dredging without restoring the floodplain and reducing sediment upstream will result in a temporary fix.

Clearing the channel could give the steelhead, which are listed as threatened by federal regulators, and other fish somewhere to escape when breaches occur, said Chris Spohrer, acting director of the agency’s Santa Cruz district since January.

New Year Uncorks the Creek