Since
1988, the District has managed the McNabney marsh jointly with the East
Bay Regional Parks District, the Contra Costa County Mosquito and
Vector
Control District and the California Department of Fish and Game. The Mt. View Sanitary District treatment plant effluent flows into a series of marshes, rather than into a deep-water outfall as most treated wastewater does. These marshes, enhanced by the reclaimed effluent, are rich and diverse in wildlife and easily accessible to visitors-recreational, scientific and student. The marshes support a variety of aquatic invertebrates, waterfowl, and other wildlife dependent on marsh habitat. Biologists have identified in the marsh 123 species of birds, 69 species of plants, 26 species of mammals and 34 species of aquatic invertebrates. At least 13 species of birds find the marshes suitable for nesting.
The District manages two distinct wetland areas that receive
all of
the treatment plant effluent-the 21-acre, constructed Moorhen Marsh and
the130-acre McNabney Marsh. Since
1988, the District has managed the McNabney marsh jointly with the East
Bay Regional Parks District, the Contra Costa County Mosquito and
Vector
Control District and the California Department of Fish and Game.
The bird watchers are the top recreational users of the marsh. The McNabney marsh entices wigeon, green-winged teal, sandpipers, shovelers, and pintail to feed and rest here during their winter migration. Unusual birds show up in the fall through early spring. In seasons past, red-shouldered hawks, stilt, sandpipers and European wigeons have visited the marsh.
The McNabney marsh is part of the larger Peyton Slough Marsh
complex.
It has been cut off from the whole of the marsh since the early 1900's.
This has restricted its ability to flood and drain with the tides and
produced
less than optimal conditions as a marsh habitat. The southern portion
(the
part along the entry road to the treatment plant) of the marsh will not
drain completely. This water sits on the soil and slowly evaporates. As
the water evaporates, salts concentrate in the soil and rise to a
concentration
that prevents any plant from growing. In the northern portion of the
marsh,
the water flows out rapidly, and salinity remains low. This part also
does
not drain, but since the water is constantly being replaced, the
salinity
is low. This creates shallow, constantly flooded conditions that
cattails
thrive in. Cattails grow so rapidly that they threaten to exclude other
plants. While cattails provide cover, the expanse of a single species
will
limit the habitat conditions. 
This year the marsh started its new flooding and draining regime. New tide gates allow a larger volume of water to flow in and out of the marsh during a tide cycle and the gates allow complete draining of parts of the marsh. Three gates will close as tides rise on their downstream side and open as tides subside on their downstream side. This prevents salt water from entering the upstream sections of the marsh. But two of the new gates are adjustable with floats. They can be set to open for part of a tide cycle and then close during another part of the cycle; this actionn allows the marsh to be flooded with salt water, without flooding the nearby streets.
The gates will allow drying of sections of the marsh overrun by cattails. The dry conditions will prevent the spread of cattails, which would eventually take over the whole flooded area. In about 2 years, tidal action may be permitted to extend throughout the marsh. This will flush the excessively saline soil in the southern portions of the marsh and encourage the development of a variety of vegetation habitats. In the lower parts of the marsh, alternating dry conditions with flooding with saline water will inhibit the encroachment of cattails. If cattails are allowed to grow without control they will tend to crowd out other vegetation. Habitats of one vegetation are less productive and beneficial than habitats with a variety of vegetation. With good variety in vegetation comes a good variety of animal inhabitants.
The spring bird censuses included sighting four Bonaparte's gulls and one Caspian tern. The Caspian terns have visited the McNabney marsh every spring for the last few years but the Bonaparte's gulls are new additions to the bird list. Great Blue Herons have been sighted in greater numbers than ever. In June and July, at least 12 blue herons were seen feeding, resting or hiding in McNabney Marsh.
The marshes are open to individual visitors from 6:00am to 4:30pm on weekdays. Leaders of large groups should call ahead to check that plant operations or other visiting groups will not interfere with their visit. Larger groups may also arrange for weekend and holiday visits by calling a few days in advance.