Southern California's best-studied wetland restoration site is in the Sweetwater Marsh National Wildlife Refuge, which includes 128 ha of wetlands (mostly intertidal salt marsh) and some uplands along the eastern side of San Diego Bay, California (32°38´N, 117°6´W). The site and the restoration project are both significant—the wetland provides habitat for endangered species and thus is critical for maintaining regional biodiversity; the project has exceptionally high criteria for judging success and thus serves as a model for future restorations.

Protection of the site and strict standards for restoration came about only after a lengthy court battle. The new refuge was designated after a federal district court (Thompson, 1988) settled a lawsuit filed by the Sierra Club and the League for Coastal Protection against three federal agencies. Wetland habitat had been damaged by construction of a wider freeway, a new freeway interchange, and a flood control channel. Endangered species had been jeopardized, and mitigation measures had not been implemented. The lawsuit also led to reinitiation of consultations and a new biological opinion by the U.S. Fish and Wildlife Service (1988), which included strict criteria for successful mitigation. The requirements were expanded to include functional wetlands that would support persistent populations of three endangered species, the lightfooted clapper rail (Rallus longirostris levipes) , the California least tern (Sterna antillarum browni), and the salt marsh bird's beak (Cordylanthus maritimus ssp. maritimus).

The current shoreline of San Diego Bay bears little resemblance to what was once the natural landscape. The bay entrance to Paradise Creek marsh has been filled, and tidal flushing has been rerouted through a channel dredged straight south to the Sweetwater River. A railroad and Interstate 5 cross the landward edge of the refuge and wetlands.

The alterations preceding the restoration/mitigation project included widening of Interstate 5, construction of a new freeway interchange, and excavation of a new flood control channel through existing wetland. Restoration began in fall 1984 with the excavation of about 4.9 ha of disturbed upper intertidal marsh, including areas previously used as an urban dump. Eight lower intertidal islands and adjacent channels