Then again, the San Onofre nuclear power plant didn't even start building its wetlands until 2006, decades after it started operating. Today, the company is roughly half-finished restoring a tidal wetland in and around the city of Del Mar, bringing back to life an area that has been all but destroyed by roads, freeways, an airport and subdivisions. Biologists for the Coastal Commission hope this project will serve as a model for Poseidon.

"We've had some disagreements, but all in all, I think they are doing a masterful job," Raimondi says of the San Onofre wetlands restoration. He adds that Poseidon's wetlands restoration, if it goes as planned, will compensate for the plant's effects on fish. "The wetlands along the coast are so degraded, we need to fix them. This may not be the p.c. way to do them, but it may be the only way."

A recent federal court ruling, however, says those efforts may not be enough. The 2007 Riverkeeper II ruling curbed the freewheeling use of seawater intakes to bring in power-plant cooling water, and required the "best technology available." Plants must recycle the seawater, or install a dry cooling system that runs boiler steam through radiator-like coils. The ruling also made it clear that creating wetlands or other manmade projects to offset the fish kills wasn't enough.

As a result, the Encina Power Plant, for one, plans to modify its plant with a dry cooling system in the next few years. A quarter of all coastal California plants have said they'll shift to less damaging cooling methods, says Tom Luster, a Coastal Commission staffer. Unfortunately, desalination plants will not be able to piggyback onto those systems because the dry cooling technology won't supply enough water. Instead, the new desalting plants will have to rely on the same fish-inhaling intake pipes that the old power plants did.

Whether Riverkeeper applies to desalination plants is still up in the air; the ruling doesn't specifically mention them. But an analogous state law does cover desalination plants, and it is stronger than the federal Clean Water Act. Environmentalists have sued to get Riverkeeper applied to Poseidon, and if they succeed, it will likely put the kibosh on the plant.

"There's so few fish left," says Conner Everts, a Santa Monica activist who grew up in Southern California during the 1950s and '60s. "When I was young, we were catching yellowtail, bonita, halibut and sand bass off the piers out here. You rarely see those anymore. The stuff they catch now -- Spanish mackerel, croaker, Tommy cod -- they are small fish that we would have thrown back or used for bait."

Everts is director of the Southern California Watershed Alliance and co-chair of a coalition of environmental groups that questions desalination. He works in a cubbyhole of an office space in the back of a Santa Monica storefront. He was schooled in conservation back in the 1970s, when he worked on the Maine homestead of back-to-the-land pioneers Helen and Scott Nearing. He later worked for the city of Pasadena as a consultant. While there, Everts engineered a host of conservation programs during an extended drought, bringing the city's total water use down by 27 percent from 1986 to 1991. His staff installed low-flow toilets and worked with commercial laundries, the Rose Bowl, golf courses and restaurants to get them to conserve.

Conservation, he says, is the answer to Carlsbad's water problems, not desalination. Each person in San Diego County uses between 175 to 185 gallons per day, he says, compared to 128 daily inside the city of Los Angeles. By simply cutting its water use to L.A.'s levels, Carlsbad alone could save some 5 million gallons of water each day, reducing the need to turn ocean water into drinking water.

Proponents of the plant see things differently, however. For them, every drop of ocean water that's desalted results in another drop of water that is not imported from elsewhere. Less water would need to be pumped from the north or the east, meaning reduced demand on the Colorado River and California Delta, less energy use, and a decrease in the quantities of greenhouse gases spewed into the air.

Still, the 4,000 kilowatt hours or more that it takes to desalt an acre-foot of ocean water is about twice the power it takes to get an acre-foot of Colorado River water to San Diego County, according to the Pacific Institute, an environmental and economic think tank. So to make up for the difference, Poseidon says it will also rely on solar power and invest in a variety of carbon offset projects.

Critics, however, point out that any imported water that is given up by the utilities that opt for desalination will soon be gobbled by growth here or elsewhere. After all, throwing water at Southern California and asking it not to use it to grow is akin to throwing oxygen and tinder-dry brush at a wildfire and asking it not to burn it up. So even a giant desalination plant producing at full capacity may not ultimately reduce demand on other water sources.