Napa Marshes Waterfowl Management Area

While the management area is quite extensive, covering much of the Sonoma Creek and Napa River flood-plain (see Steamboat Slough), there is relatively little undisturbed marsh in the inland portions (see Bull Island, Coon Island – Fly Bay and Fagan – Steamboat Slough and Marsh) though there is a well-developed salt marsh fringing the Bay (see, also, San Pablo Bay National Wildlife Refuge) and in the broad lower portions of the river. There are, however, several miles of creeks, sloughs and other open water fringed with marshes and mudflats of varying sizes that provide excellent habitats. Communities include mudflats, salt and freshwater marshes, and uplands.

Though frequently barren, the mudflats support some algae forms. In the saltwater marshes pickleweed, Salicornia virginica, salt grass, Distichlis spicata, and cordgrass, Spartina foliosa, are conspicuous, with Frankenia salina on the margins. Five species of bulrush are found in the area, with Scirpus robustus common in both the salt and freshwater marshes; other forms include Scirpus californicus, Scirpus olneyi, Scirpus acutus, and Scirpus americanus. Cattails are common in the freshwater marshes and fringing areas and include both Typha angustifolia and Typha latifolia. In the upland areas and along the levees coyote bush, Baccharis pilularis and Baccharis douglasii, and yarrow, Achillea millefolium are conspicuous.

A wide variety of birds has been reported from these marshes and uplands, with shorebirds and waterfowl the most numerous. Among the ducks, the canvasback, Aythya valisineria, is the commonest in season. Other birds of note include the tricolored blackbird, Agelaius tricolor, and the white-tailed kite, Elanus leucurus. This area is one of the main remaining habitats of the endangered California clapper rail, Rallus longirostris obsoletus.

Rodents constitute the main mammal population. The endangered salt-marsh harvest mouse, Reithrodontomys raviventris, is found in various localities within the area.

At least 11 species of fish have been identified as inhabiting the sloughs of the marshes, the most common being the introduced striped bass, Roccus gaxatilis, some of which spawn here. Other of the more common fish include the threadfin shad, Dorosoma petenense, starry flounder, Platichthys stellatus, jacksmelt, Atherinops californiensis, tule perch, Hysterocarpus traski, and American shad, Alosa sapidissima.

The entire area lies in the floodplain and is formed of Quaternary alluvium.

Integrity: In the 1870's the marsh area occupied all of the floodplain but diking has converted perhaps 80% of the area into crop land and salt ponds. There are various buildings, roads and railroads within the area.

Use: Educational, research, light recreational, hunting, fishing, on public portion; remainder, private.

February 1976