Environmental Mike Prather stands in the Owens River, which contains water for the first time since 1913, when Los Angeles diverted the water into its aqueduct to serve its growing population. (By John Pomfret -- The Washington Post)

"This is what I expected," Prather, a 60-year-old environmentalist, said as he and his 26-year-old daughter, a graduate student in wildlife management, watched the water seeping into the sand. "It's not a tsunami; it's more like the tide coming in. I am going to remember this moment for the rest of my life."

Water was returned to the Owens River on Dec. 6, when Los Angeles Mayor Antonio Villaraigosa and Inyo County Supervisor Susan Cash symbolically concluded the most celebrated water war in American history.

Almost a century after Los Angeles diverted the Owens River into the city's aqueduct, Villaraigosa and Cash opened a gate and allowed some of that water to return to the river, starting a reclamation effort (62 riparian miles, 30 air miles) rivaled only by the Kissimmee River Restoration Project in the Florida Everglades.

Traveling less than one mile a day, the flow by a recent Friday had reached a spot on the old riverbed just a few miles north of Independence, where Prather found it.

"By restoring the lower Owens River, the city of Los Angeles will do more than right an historic wrong," Villaraigosa said at a ceremony marking the beginning of the project. "In a deeper sense, we will affirm a literal truth: that when it comes to protecting our environment, it is time for all of us to change course."

The story of the Owens River Valley and Los Angeles is one of the great narratives of the West, chronicled in the 1974 Hollywood classic "Chinatown." Starting in 1904, agents for the city of Los Angeles masquerading as businessmen and ranchers snapped up hundreds of thousands of acres in the valley, 230 miles north of the city.

Los Angeles built an aqueduct and in 1913 diverted the Owens River, which is fed by the snowpack on the Sierra Nevada Mountains to the west, to slake its growing thirst. Another boom in the 1960s prompted the city to pump out the valley's ground water; a second aqueduct was completed in 1970. In total, the aqueducts deliver more than 430 million gallons a day to the city -- 70 percent of its water needs.

"Los Angeles employed chicanery, subterfuge, spies, bribery, a campaign of divide-and-conquer and a strategy of lies to get the water out," wrote the late Marc Reisner in his 1986 book, "Cadillac Desert." "In the end, it milked the valley bone-dry."

Springs that annually transformed the valley into a rich marshland for migrating birds, bobcats, deer, elk and mountain lions dried up. Salt grass, cottonwoods and willows died off; tumbleweed and salt cedar moved in.

But the fact that the Los Angeles Department of Water and Power (DWP) owned all the land meant that the valley was saved from the city's sprawl. No strip malls or gated communities mar the landscape. To this day, Inyo County's 18,000 residents live on 1.7 percent of the land.

Starting in the 1970s, environmentalists and residents of towns along the valley began suing the DWP to force it to return water to the valley.

In 1997, the DWP reached an agreement with plaintiffs in the case, including environmental groups such as the Sierra Club and the Owens Valley Committee, to re-create a healthy and diverse habitat for fish, waterfowl and shorebirds by mid-2003.

The city also agreed to place more than 300,000 acres of land it leases to ranchers under a strict management program. And it agreed to mimic the seasonal flooding of the grasslands, which would again turn chunks of the valley floor into fecund marshland, with scheduled releases of water from the aqueducts.

But the DWP dithered. Finally, on July 26, 2005, Inyo County Superior Court Judge Lee E. Cooper vowed that "no excuses will be expected" and ordered the second aqueduct shut down unless Los Angeles began returning water to the valley.

Under current plans, the Owens River will run only two feet deep. But that is enough water to allow some habitats to regenerate, and the seasonal water surges will push seeds even farther out along the riverbanks.

Although the judge's decision forced Los Angeles to act, other developments also made it possible. The city's water conservation efforts have been some of the most successful in the nation; over the past 20 years, while Los Angeles has added 750,000 homes, its water consumption has remained the same. Its water commission used to be dominated by urban boosters, but with time, environmentalists invaded its ranks.

Finally, the DWP itself has changed. "It used to be all engineers," said Prather, "but now they have biologists and wildlife managers."

The Owens River was not the only court defeat handed to the DWP. In the 1990s, a court forced Los Angeles to begin returning water to Mono Lake, a once-pristine ecosystem north of Owens Valley. Over the years, the lake's water table dropped 41 feet because of the city's unquenchable thirst. But in recent years, the water level has risen 10 feet.

On a separate track, lawsuits also went after the DWP because diverting the Owens River had dried up Owens Lake, causing one of the most serious dust pollution problems in the nation -- routinely 30 times higher than federal limits. The U.S. Geological Survey called the lake "possibly the greatest or most intense human-disturbed dust source on Earth."

In a court deal in 1999, Los Angeles agreed to mitigate the dust by flooding, spreading gravel or seeding the lake bed. The DWP installed "bubblers," industrial-size sprinklers, to dampen it. So far, it has spent $400 million mitigating the dust, and particulate matter has dropped by 60 percent. In all, more than 30 square miles of the lake will be irrigated. And once water reaches the lake by way of the reopened riverbed, it will be used to further limit the lake bed's dust.

The wetting of Owens Lake has had another fortuitous outcome. It has prompted tens of thousands of birds to return to the region to feast on freshwater shrimp and brine flies. The Owens Valley Committee has documented 39 types of birds, including 26 species of waterfowl, 16 species of birds of prey, 33 species of shorebirds, five species of owls and a coyote living on ducks on an island in the middle of the lake, Prather said.

"Nature is pretty forgiving if you give it a chance," he said as he watched a black-and-white American avocet pick through the mud. "In five years, this valley will be completely transformed."