Butte Sink Wildlife Management Area has the highest concentration of waterfowl per acre in the world. Located in the Sacramento Valley of California, it includes the Butte Sink National Wildlife Refuge and conservation easements acquired on adjacent private lands. The landscape is flat, bordered by the Sierra Nevada and Coast ranges, and surrounded by intensive agriculture (primarily rice and nut orchards).

Within the 18,000 acre Wildlife Management Area, conservation easements have been purchased on 10,311 acres, requiring landowners to maintain wetlands on their property in perpetuity. These lands are privately owned and closed to public access. In addition, a 733-acre area (owned in fee title) was established in 1980 to protect wetlands for wintering waterfowl. This area is known as the "Butte Sink NWR" and is also closed to public access.

Major refuge objectives are to provide feeding and resting habitat for wintering waterfowl; provide habitat and management for endangered, threatened, or sensitive species of concern; protect and provide habitat for neotropical migratory land birds; preserve a natural diversity and abundance of flora and fauna; and alleviate crop depredation.

The Butte Sink typically supports wintering populations of over 300,000 ducks and 100,000 geese. As 95 percent of wetlands of the Central Valley have been lost over the last 100 years, waterfowl have become increasingly dependent on the remaining wetlands within the Sacramento Valley.

These privately-owned lands are closed to the public.