Neighbors of the reserve, south of the port of Long Beach, cheered and sipped champagne (at 7 a.m.) as the salty water poured into the fragile ecosystem.

The eight state and federal agencies involved in the project call it the largest and most ambitious restoration of coastal wetlands in the history of California, where 95 percent of saltwater marshes have been given over to development.

The Bolsa Chica wetlands project is at the cutting edge of a new and evolving science, said Shirley Dettloff, a member of the conservation group Amigos de Bolsa Chica and a former member of the California Coastal Commission.

“Not many wetlands have been restored in the world, especially in an oil field,” said Dettloff.

At one time, as many as 4,884 homes were proposed on 1,100 acres of the wetlands. The plan was scaled back to 3,300 homes by 1996.

Now, homebuilding is confined to the upper mesa area of Bolsa Chica, with a 356-home development under way.