Moorhen Marsh

Moorhen Marsh facing west towards the Shell Martinez Refinery which surrounds the marsh on two sides.

Moorhen Marsh facing west towards the Shell Martinez Refinery which surrounds the marsh on two sides.

In 1974, MVSD created Moorhen Marsh, the first wetlands on the west coast dependent solely on treated effluent s as its primary water source. The 21-acre constructed wetland saved the District’s rate payers millions of dollars by avoiding the construction of a deep-water outfall to transport MVSD’s treated wastewater to the Carquinez Strait, all while creating critical habitat for wildlife. Native wildlife species dependent on the wetland for habitat includes the western pond turtle, North American river otter, mink, North American beaver, and many species of birds including marsh wren, San Francisco common yellow-throat, Suisun song sparrow, green heron, snowy egret, and black-crowned night heron.

A female western pond turtle looking for a dry place to dig her nest in Moorhen Marsh.

A female western pond turtle looking for a dry place to dig her nest in Moorhen Marsh.

In the San Francisco Bay Area, where most freshwater wetlands have been lost, Moorhen Marsh is a shining example of a community success story. It provides important open space in a heavily industrialized area, while also offering educational opportunities for over 1600 elementary, secondary, and college students every year. Birders, photographers, hikers and families also enjoy Moorhen Marsh. Moorhen Marsh also functions in the treatment process by reducing ammonia as the effluent travels through the wetland before flowing into Peyton Slough and eventually out to the Carquinez Strait.

Moorhen Marsh is completely dependent on MVSD’s advanced secondarily treated effluent for its water. Without the approximately 1.2 million gallons of effluent provided by MVSD’s treatment plant every day, this historic marsh would cease to exist. The marsh is open to the public during business hours only: Monday – Thursday, 7:00 am – 4:30 pm and Friday, 7:00 am – 3:30 pm. There is no access on the weekends or during observed holidays except on scheduled public tours or by special arrangement with the District Biologist.


For a bird checklist for Moorhen and McNabney marshes, click here.

For an aerial map of the marsh, click here.

To contact the District Biologist to report a wildlife sighting or ask a question, click here.