Tide Gates Opened at Novato Pond After Fish Kill

MARIN COUNTY, CA - Following a tip from a local resident, the Marin County Department of Public Works’ Flood Control staff is working with local government agencies to investigate a fish kill in Pacheco Pond near Novato, county officials reported Friday.

The Bel Marin Keys Community Service District reported that about 20 dead fish, likely invasive European carp, were observed Tuesday in the 120-acre pond, located off Bel Marin Keys Boulevard between the commercial district and the residential area, according to a news release.

County staff noticed large areas of algae covering the surface of the pond this week. County experts believe algal mats, or a sheet-like layer of bacteria and sediment on the water’s surface, may be contributing to the fish kill.

"As the algae breaks down it depletes oxygen in the pond, which can lead to fish kills," said Brent Ainsworth, county public information specialist. "Since that is a natural event, officials decided to let nature take its course with the fish and did not remove them from the water."

According to Ainsworth, county personnel have been keeping open the tide gates that lead to San Pablo Bay this summer to increase water levels in the pond and improve circulation. Opening the gates also mitigates the rotten-egg smell that results from an anaerobic digestion process in the water. Most of the year, no smell is noticeable because the buildup of stinky gasses stays locked away on the bottom of the pond. It is typical for ponds to “turn over” in the late summer months, releasing foul-smelling gases. To assist the pond with its natural digestion process, the county opens the tide gates at Novato Creek to improve aeration and circulation within pond.

Ainsworth said staff is coordinating its response with the Marin Sonoma Mosquito and Vector Control Board and the California Department of Fish and Wildlife. Personnel will inspect the pond and related water quality conditions on a weekly basis until the typical “turn over” period is over.

County officials asked anyone who notices dead fish in the pond to call 415-473-6528.

Photo: Pacheco Pond near Bel Marin Keys (Courtesy of County of Marin Public Information Department)