County of Marin - News Releases - Pacheco Pond Bacteria

For Immediate Release
October 01, 2015

Flood Control Works to Rid Pond of Nasty Smell

Tidal flushing should provide odor relief

San Rafael, CA – Residents of the unincorporated Bel Marin Keys neighborhood near Novato received a message this week: We know Pacheco Pond stinks, and we’re doing something about it.

Flood gates on Pacheco Pond, with marshland in foreground and Novato hills in background.The Marin County Flood Control and Water Conservation District has worked closely with the Bel Marin Keys Community Services District (CSD) to monitor water quality in the Novato Creek. 

Pacheco Pond, which is managed by County Flood Control, is located between the commercial section of Novato and the Bel Marin Keys community of homes near the Hamilton Wetlands Preserve. Pacheco Pond has been particularly pungent the past few weeks, providing a familiar fall funk for drivers along Highway 37 and other areas around southern Novato. As autumn air temperatures drop, the upper layers of the 120-acre pond water grow colder and heavier. The upper water sinks and mixes with the layers below. With no circulation, the oxygen is quickly used up, resulting in a stinky pond. The pond presently has a high bacterial component.

The pond bacteria use enzymes to ferment and digest the muck on the bottom of the pond, and their waste products include hydrogen sulfide, notoriously renowned for its rotten egg smell. Most of the year, no smell is noticeable because the buildup of stinky gasses stays locked away on the bottom, but the stinky gas is released when the pond “turns over.” The resulting emanation can singe the sinus cavity and crinkle the nose of anyone within about a two-mile radius.

Compounding the situation, Sago pondweed has exponentially expanded across the pond’s surface the past two years. Ducks, swans and other migratory waterfowl find the pondweed delicious, and they may have unknowingly transported the plant to Pacheco Pond. As the pondweed dies off in late summer, bacteria consume the remnants creating a smorgasbord for aquatic critters but odiferous conditions for local residents.

The two agencies are letting nearby residents know that they are coordinating their respective efforts.

County Flood Control closed its tide gates at Pacheco Pond to Novato Creek when it was determined that the creek had a high bacterial content after pond water flowed into the creek. Keeping the tidal gates closed will allow Novato Creek’s bacterial content to return to a normal range; once that happens, the Bel Marin Keys CSD will fill its lagoons with high tides from Novato Creek. It is hoped that this process will be completed in the next week.

The Bel Marin Keys CSD posted a notice September 25 about the discovered high bacteria levels in Novato Creek, prompting County Flood Control to close the tide gates. Once Bel Marin Keys CSD completes the lagoon filling, County Flood Control will open the tide gates to take advantage of the high tides to improve aeration and circulation within the pond. That should also help to mitigate the smell. After lagoon flushing is finished, County Flood Control will keep the tide gates open until rains are forecast.

Pacheco Pond falls within Zone 1 of the Marin County Flood Control and Water Conservation District, which is overseen by the Marin County Board of Supervisors. Flood Control personnel are part of the Marin County Department of Public Works team and based at the Marin County Civic Center in San Rafael.


Liz Lewis
Water Resources Manager
Public Works

3501 Civic Center Drive
Suite 304
San Rafael, CA 94903
(415) 473-7226
Email: Liz Lewis
Public Works website