A marsh is a type of wetland, an area of land where water covers the ground for long periods. A tidal marsh is found along rivers, coasts, and estuaries that floods and drains by the tidal movement of an adjacent estuary or sea. Tidal marshes serve many important functions: They slow shoreline erosion, offer shelter and nesting sites for migratory water birds; and absorb excess nutrients that would lower oxygen levels in the sea and harm wildlife.

The elevations within a tidal marsh can vary. The mid-level elevation is known as the marsh platform. As the tide ebbs in the marsh, mud flats above the platform become exposed, which contain layers of decaying organic matter that can cause a rotten egg smell. Areas below the platform experience water stagnation and algal blooms.

McNabney Marsh is a 138-acre, brackish tidal wetland. The wetland is jointly owned by MVSD and the East Bay Regional Park District. It supports many species of wildlife, including nesting shorebirds, waterfowl, and wetland songbirds. Visitors are welcome to view McNabney Marsh from the observation platform located at the end of Service Road, Mondays through Saturdays, 7am – 5pm. There is no access on Sundays or holidays.