Dan Haifley
Our Ocean Backyard:
Water and fish on the wild coast

Pescadero Marsh is a wild paradise roughly halfway between Santa Cruz and Half Moon Bay. If you have plenty of time, blue herons, kites, deer, ducks, raccoons, foxes, skunks, and egrets can be found among a beautiful variety of plants where Butano and Pescadero Creeks meet the wild Pacific.

The marsh’s vegetation and decomposing materials filter pollutants from the water. It’s also a popular spot for animals and birds that visit and feed in the beautiful landscape of native plants shaped in fertile soils by wind, sun and animals. Reader Kathy Haber asked about boats navigating the creeks back when there was less sediment, and yes, they likely did.

After winter rains and a strong tide, the sand bar that blocks the marsh from the sea opens and tidal interaction is restored. Lennie Roberts of the Committee for a Green Foothills says that water that had been stagnant during summer drains into the ocean as the first big tide goes out, stirring up some mud that creates trouble for resident steelhead and other fish.

Unfortunately during some winters opening of the sand bar has killed fish in the portion of Butano Marsh that lies between Pescadero Creek Road and Butano Creek.

“After some careful field observations and water quality sampling, local fishermen believe that as the sand bar opens the outgoing rush of water causes turbulence that stirs up fine sediments, mud and decayed bottom vegetation that mixes with the cleaner layers of water above,” says Roberts. “The smelly plume of muck releases oxygen-deficient water and hydrogen sulfide, suffocating fish and other fish species that use gills to breathe. One year, observers counted some 350 dead fish, mostly juvenile steelhead.”

An attempt over a decade ago to open levees may have unintentionally brought more sediment to where the fish kills occurred. When water levels rise in summer, leaves die and begin to decay, setting up an unintended surprise for the steelhead when the bottom layer is stirred up.

The challenge is to improve conditions for fish without harming other marsh inhabitants, such as the California red-legged frog, San Francisco garter snake, and the brackish water snail. Some have conflicting habitat requirements, so any alterations to the marsh to benefit fish will have an impact on other inhabitants.

Roberts recalls an attempt to install a water-filled membrane where the fish kills have occurred to prevent the initial rush of outgoing water from this area when the mouth opened. They would then reduce the height of the water bags gradually so the area would drain without creating turbulence, which they believed was releasing hydrogen sulfide. State Parks agreed to allow the experiment, but the bags did not stay in place.

This year the mouth of the creek did not close until October. Fisheries biologists are working to determine if the timing of closure of the mouth will affect the number of fish killed when it reopens. The marsh is a natural preserve in the California State Parks system, so one can take advantage of it and take a day to explore.