The 10,783-acre refuge consists of about 7,600 acres of intensively managed wetlands, uplands, riparian habitat, and vernal pools. It typically supports wintering populations of more than 600,000 ducks and 200,000 geese. More than 95 percent of the wetlands of the central valley have been lost in the last 100 years, and waterfowl have become increasingly dependent upon the refuges of the Sacramento Valley.

The refuge supports several endangered plants and animals, including transplanted colonies of palmate-bracted birds-beak, several species of fairy shrimp, vernal pool tadpole shrimp, giant garter snake, wintering peregrine falcon, bald eagle, and breeding tricolored blackbird. Resident wildlife includes grebe, heron, blackbird, golden eagle, beaver, muskrat, black-tailed deer, and other species typical of upland and wetland habitats. Approximately 9,000 people hunt on the refuge each year, and 73,000 people use the visitor center, auto tour route, and walking trail.

Water manipulations are most commonly used to encourage or discourage vegetation species, create suitable depths for a variety of wildlife, and to minimize mosquito production. Water is delivered through local irrigation districts. Significant quantities of vernal pool-alkali meadow habitat are naturally filled with rainwater and provide some of the highest diversities of native flora and fauna in the Sacramento Valley.

The refuge has an annual habitat management plan that sets objectives and directs management activities, prioritizing work on approximately 67 habitat units. The plan includes floodup and drawdown dates, vegetation manipulation required, levee repairs, special management considerations, and other tasks required to meet refuge objectives.

Standardized ground and aerial wildlife surveys and vegetation surveys are conducted regularly throughout the year to inventory populations and document habitat use. Each year units are evaluated by how well they met habitat and wildlife use objectives.

This information is stored in a computer database so it can be accessed, analyzed, and reported as needed. Research is encouraged; and staff is involved with initiating and conducting studies that have direct applications to management. Recent examples include studies on the effects of mosquito abatement activities on refuge biota, giant garter snake ecology, and causes of avian cholera outbreaks.