San Diego Bay National Wildlife Refuge, Nature reserve in Imperial Beach, United States

San Diego Bay National Wildlife Refuge is an urban refuge of 316 acres of salt marsh and coastal uplands on San Diego Bay, split between the Sweetwater Marsh Unit on the east side and the 2,300-acre South San Diego Bay Unit. Over 90 percent of the bay's historic wetlands have been filled, drained or diked, so the refuge restores tidal flats, mudflats and eelgrass beds within an approved boundary of 2,620 acres. Its sign at the edge bears the crossed-shovels Coronado Railroad emblem and the heading "Bridging History".

The 316-acre Sweetwater Marsh Unit was established in 1988 on the east side of San Diego Bay, and the refuge now hosts the headquarters of the San Diego National Wildlife Refuge Complex. The Kumeyaay people first used the area for fishing, hunting and gathering. From 1916 to 1920 a 30-acre kelp-processing plant of the Hercules Powder Company made acetone and potash on the site. The 2,300-acre South San Diego Bay Unit was dedicated in 1999.

The Living Coast Discovery Center within this refuge offers visitors a chance to learn about local wildlife through exhibitions and guided tours. This educational hub attracts school groups and nature enthusiasts interested in understanding the habitats around them.

Visitors can reach the refuge trails via free shuttle service from the Living Coast Discovery Center or explore the area using the Bayshore Bikeway. Early morning hours offer the best wildlife viewing, when animals are most active and visible.

The refuge is home to more than 200 bird species and provides a critical refuge for four endangered animals, including the California least tern. This small seabird once nested at only a handful of locations along the California coast and remains one of North America's rarest tern species.