Tijuana Slough National Wildlife Refuge protects the northern part of the Tijuana River estuary in San Diego, California, at the southwestern edge of the contiguous United States. Established in 1980, it preserves one of Southern California’s largest remaining uninterrupted salt marshes in a heavily urbanized border region. That habitat supports migrating shorebirds and waterfowl along the Pacific Flyway, with more than 370 bird species recorded there, and it is especially important for endangered birds and plants. Its work focuses on research, habitat restoration, and environmental education to improve estuary health, while its inclusion in larger reserve and refuge networks underscores its regional and national conservation significance.