McNabney Marsh (formerly known as Shell Marsh) is a restored, muted tidal wetland located east of I-680 in Martinez. The 138-acre wetland is jointly owned by MVSD and the East Bay Regional Park District, with an agreement that gives MVSD full responsibility for its management.
Historically, McNabney was a brackish tidal marsh linked to the Carquinez Strait. In the late 1880s, McNabney was diked and separated from the Strait by the construction of a Union Pacific Railroad line. Hydrology of the site was further altered in the 20th century by the construction of roads and highways, pipelines, and mosquito abatement ditches. As a result, the site was converted to pasture land for almost a century.
MVSD purchased its 69 acres of McNabney in the 1980s. Supplied by MVSD’s freshwater discharge, the site effectively functioned as a freshwater marsh that supported many species of nesting birds, mammals, fish, and plants. Though some residual salts in the soils may have persisted, the vegetation community was characterized by freshwater vegetation. Over the past decades, the marsh has significantly sunk, and MVSD estimated that as much as three feet of elevation to the marsh plain was lost. With the increased subsidence and adjacent infrastructure, managing the marsh for increased habitat function and value has been difficult.
Challenges increased even further with the operation of the Peyton Slough tide gates in June 2009. Although the tide gates have allowed some brackish marsh features to return, it has also increased water stagnation, algal blooms, nuisance odors, and decreased ground nesting habitat for waterfowl and shorebirds. Additionally, the tide gates are operated by a third party whose primary interest is managing a pickleweed marsh mitigation site. Because of both historical and current conditions, McNabney poses many significant management challenges. These issues will need to be addressed if the wetland is to flourish both as a habitat for fish and wildlife and as a prominent site for recreational and educational opportunities for the local community.
With this in mind, MVSD is working with Ducks Unlimited Inc., (DU) to create a management plan for the site. DU is a well-regarded non-profit with significant experience in restoring and enhancing wetlands across the county. Draft documents for the management plan are available: