Green Island is an island in the Napa River, upstream of San Pablo Bay (an embayment of San Francisco Bay). It is in Napa County, California, and managed as part of the Napa-Sonoma Marshes Wildlife Area. Its coordinates are 38°12′09″N 122°18′16″W / 38.20250°N 122.30444°W / 38.20250; -122.30444 (Green Island), and the United States Geological Survey measured its elevation as 23 ft (7.0 m) in 1981. It, long with Island No. 1, Island No. 2 and Tubbs Island, are labeled on a 1902 USGS map of the area.