In November 1980, the writer Philip Fradkin kayaked into the Delta and floundered through an apocalyptic landscape that pushed him to the edge of panic. Starved of water for more than four decades, the lush forests had given way to vast, desolate mudflats. Fradkin recounted his nightmarish journey in his book A River No More, which stands as a kind of epitaph for the Delta.

That same year, Lake Powell – after slowly impounding 8.5 trillion gallons of water over the previous 17 years – finally filled to the brim. Soon after, a strong, wet El Niño weather system took hold of the West. In 1983, winter storms dumped so much precipitation into the Colorado River Basin that its dams couldn't hold back all the spring meltwater. To keep Glen Canyon Dam from disintegrating, engineers opened its spillways and sent 3.6 million acre-feet blasting downstream. And so, as Fradkin wrote in an updated version of his book, "The river momentarily roared back to life and punched its way through to the Gulf of California."

Ed Glenn happened to be down in the Delta when the flood ripped through. "The levees all failed and the water went everywhere," recalls the University of Arizona biologist. "I saw water from one edge of the Delta to the other."

In the years afterward, Glenn worked primarily in a nearby marsh called the Ciénega de Santa Clara, and didn't think much about what was happening in the Delta itself. But in 1992, as he was leaving Mexico for Tucson aboard a private aircraft, "we decided to fly the plane up the river."

Where he had expected to see only mudflats, Glenn saw something astounding. "Those trees," he remembers thinking, "aren't supposed to be there."

Intrigued, he secured a grant from NASA, enlisted the help of several colleagues and began, as he puts it, "just gradually putting the story together."

During the early and mid-'80s, El Niño had consistently sent water roaring down into the Delta and fanning out across its floodplain. And the dynamics that drove life there for millions of years suddenly revived: As those pulses of water receded and evaporated, seeds rained down from remnant stands of cottonwoods and willows, landed in the moist soil of the floodplain, and sprouted.

"The roots can grow an inch a day," Glenn says, "so they're able to follow the drying soil down to the water table. By the end of the first year, they're tapped in." Less than a year after a flood, seedlings can reach six or seven feet; by the end of the second year, they're as tall as 35 feet.

With this revelation, Glenn, Zamora and their allies began campaigning to raise awareness about the possibilities of restoring the Delta, patiently lobbying for a dedicated flow of water. At the same time, other groups pushed harder.

In 2000, Defenders of Wildlife and several other environmental organizations sued the U.S. government, arguing that it was ignoring the harm its dams were causing to endangered birds, such as the southwest willow flycatcher and Yuma clapper rail, which are protected under U.S. law but also live across the border, in the Delta. In court, the U.S. successfully argued that its obligations under the Endangered Species Act stop at the border, and that the so-called "law of the river" – the complex body of agreements, treaties and court cases that governs the Colorado – is so ironclad that the government lacks "discretionary authority" to provide water for the Delta.

Yet the government did compromise slightly. In December 2000, the U.S. and Mexico signed an amendment to the 1944 treaty that stipulates how the river's water is divided between the two countries. Known as Minute 306, the agreement offered a first, tentative acknowledgment of the Delta's ecological importance, as the two nations pledged to "formulate recommendations for cooperative projects concerning the Colorado River Delta in Mexico."

But Minute 306 appeared just as the drought set in. In 2000, Lake Powell received just 62 percent of its annual average inflow. In 2001, inflow was 59 percent of average. Then, in 2002, it plunged to a mere 25 percent of average. Water managers shifted into crisis mode and launched an effort to plug every leak in the system, repair any remaining inefficiencies, and intercept every last drop of runaway water that was slipping across the border – the very same water that was keeping the Delta alive.

The main target of that push was the All-American Canal, which carries water along the U.S.-Mexico border from the Colorado River to farmers in Southern California. Some 190,000 acre-feet of water – more than the city of Tucson uses – seeped from the canal into the ground each year. So, in 2003, U.S. water agencies announced they would spend $300 million to line it with concrete.

There was a hitch, though: Almost all of that leaking water flowed to farms and wetlands in Mexico's Mexicali Valley. Mexico fought to stop the project, and the battle dragged on in court for three years. Believing legal resolution was hopeless, the water agencies turned to Congress. And on Dec. 8, 2006, legislators passed a rider to a tax-and-healthcare bill that ordered the project forward – a political poke in the eye for Mexico that, for good measure, also authorized a new reservoir to vacuum up any extra water that may have inadvertently slipped away toward Mexico and the Delta.