Twitchell Island, River delta island near Sacramento, United States.

Twitchell Island is a river delta island in the Sacramento-San Joaquin delta region, located southwest of Sacramento and mostly composed of peat soil. The area is shaped by managed practices that balance farming with environmental goals.

Twitchell Island was reclaimed from tidal marsh for farming, with drainage and levee work reshaping the peat soil. The land is now managed by Reclamation District 1601, and the State of California owns about 85 percent of the island. The island lies entirely within the Rio Vista Gas Field, though well pads and related infrastructure occupy only a small part of its land.

The island's name comes from the Twitchell family, early Delta landowners. Since 1996 the U.S. Geological Survey has grown tules and cattails on a 15-acre plot, and the peat surface there has risen 1 to 2 feet. The plants also store carbon, a fact cited in Delta wetland debates.

Access is controlled by local authorities and limited due to environmental protections in place. Visitors should check in advance whether and how the area can be visited.

Since 1996, scientists have been studying whether planting tules and cattails can reverse soil loss on the island. These long-term studies help explain how wetlands naturally store carbon.