San Diego Bay National Wildlife Refuge, established in 1988, protects one of the last major remnants of salt marsh and coastal upland habitat on a bay where more than 90 percent of historic wetlands have been lost. Centered first on the 316-acre Sweetwater Marsh Unit and later expanded with the 2,300-acre South San Diego Bay Unit, it preserves and restores marshes, mudflats, eelgrass beds, and native uplands for resident and migratory birds, waterfowl, and native fish. The area also reflects earlier Kumeyaay use and industrial activity, and it shelters rare and endangered species while facing threats from sea level rise, drought, and wildfire.