The tiny green shoots that fringe a lagoon on a meander of the Colorado River here may not look like much, but they offer great hope.

As Tomás Rivas of the Sonoran Institute, a U.S. conservation group, points out the small cluster of willow seedlings, he spots a movement through the patch of green, then another. Two lowland leopard frogs are leaping through the lattice of twigs at the edge of the water.

“That’s a good sign,” says Rivas, a habitat-restoration specialist, following the amphibians’ tracks with the long lens of his camera.

The frogs represent small victories in a much larger task: restoring parts of the natural habitat of the once-lush and well-watered Colorado River delta, now a dry wasteland where there is neither river nor delta to speak of. For eight weeks this spring, all that changed when the floodgates opened on the Morelos Dam, the river’s southernmost barrier, sending a surge of water through the desert riverbed.

The pulse flow, as the water release is called, was intended to mimic the effect of the spring snowmelt, which used to swell the Colorado’s course just as the willows and cottonwoods on the river banks released their seeds in the humid soil.

“It doesn’t need to happen every year,” says Jennifer Pitt, director of the Colorado River Project for the Environmental Defense Fund. “Every four or five years; that would be sufficient to maintain the habitat ... That’s the premise. We have a lot to study.”

What conservationists hope is that the pulse flow, which has now been followed by a permanent smaller base flow to maintain shallow ground water, will create conditions for the native trees to take root and flourish, recreating riparian corridor habitat for birds, mammals and other wildlife.

“I don’t like to call this an experiment because experiments can work or they can fail,” says Francisco Bernal, the Mexicali representative for the International Boundary and Water Commission (IBWC), the binational organization that manages the border-water treaties between Mexico and the United States. “We did this as an exercise believing that it would work.”

By all accounts, the pulse flow that began on March 23 succeeded better than anyone had dared to hope. Over the eight weeks, 104,000 acre-feet (about 130 million cubic meters) of water swirled into the sandy ditch that is the Colorado’s course in Mexico.

The water reached the driest portions of the river and still it flowed, continuing downstream to cover 60 miles of riparian habitat in all. Birds returned, the ground water rose, and the existing conservation sites became lush with wildlife.

It was the first time in two decades that communities have seen the river that once sustained them. People jumped into the river with excitement.

“It’s a new beginning,” says Francisco Zamora, director of the Sonoran Institute’s Colorado River delta efforts. “It was a key point in the history of the delta.”

On May 15, after a new release of water from irrigation canals below the dam, the river finally reached the Gulf of California, about 94 miles downstream. It was a symbolic restoration of the river’s course and a glimpse of a future in which important fish species in the upper gulf, such as Gulf corvina (Cynoscion othonopterus) and the endangered totoaba (Totoaba macdonaldi), may one day be bolstered by restoration of the Colorado delta. “That was the icing on the cake,” says Zamora. “What it shows is that it can be done.”

Agrees Pitt: “We just demonstrated that there may be a path forward. That success may be enough to win a longer-term commitment from governments on both sides of the border to commit to sustaining the habitat.”

Though the pulse flow lasted only eight weeks, scientists are following its effects closely to see how long they will last. This means counting birds and other wildlife, measuring surface water and groundwater and monitoring seedlings to see how well years of planning, coaxing and negotiating have paid off.

At the Laguna Grande restoration site, where Pronatura, a leading Mexican conservation group, and the Sonoran Institute have been working on 200 hectares since 2008, there are hints of what can be accomplished.

Seepage from agricultural irrigation and new channels that the conservation groups have dug bring water to a modest lagoon here in an old meander of the river. The pulse flow connected the lagoon to the main river channel and filled it with life. Dragonflies dart over the surface, egrets are poised on the shore and an American coot paddles serenely through the water, followed by its young.

The pulse flow “surpassed anything we had thought at the beginning,” says Rivas.

Alongside the lagoon, the conservationists have planted a dense forest of willow and cottonwood that has reached 15 to 18 meters high after just three years. As Rivas leads the way, he identifies the call of a mourning dove and a white-winged dove. The forest has become a hub for birds, including the willow flycatcher and yellow-billed cuckoo, which are endangered.

The forest is also home to quail, pheasant, and small mammals including raccoons and gophers, their presence registered by motion-activated cameras. Bobcats and coyotes occasionally lope through.

“The birds arrived almost immediately,” says Alejandra Calvo Fonseca, who oversees wildlife monitoring for Pronatura. By October, she expects to have a better idea of how well the seedlings have survived. “This gives us a guide to management in the future,” she says.

A century ago, the lagoons and fingers and oxbows of the Colorado River delta reached across 2 million acres in the Mexican states of Baja California and Sonora. The conservationist Aldo Leopold explored it by canoe in 1922 and recalled more than 25 years later in his classic “A Sand County Almanac” that “the river was nowhere and everywhere.”

Imagining the trip of the first Spanish explorer to travel through its “hundred green lagoons,” Leopold wrote: “He divided and rejoined, he twisted and turned, he meandered in awesome jungles, he all but ran in circles, he dallied with lovely groves, he got lost and was glad of it and so were we.”

But the “milk and honey wilderness” he described, was about to disappear. From the 1930s to the 1960s, the U.S. course of the Colorado River was segmented by dams and the reservoirs bulging behind them. Its water was siphoned off to quench the thirst of booming cities in California and the Southwest and irrigate the farms of central Arizona and California’s Imperial Valley.

When the river at last reaches Mexico, the Morelos Dam forces the water into a sharp turn to the west, into a crisscross of irrigation canals that feed the Mexicali Valley’s fertile fields of cotton, wheat and alfalfa. By the 1960s, the delta had gone dry, leaving what is now a variegated patchwork of irrigated fields transected by a brown gash—what’s left of the river’s course. Even before all the dams were completed, Leopold knew that the delta could not survive. His 1949 essay concludes: “I am told the green lagoons now raise cantaloupes. If so, they should not lack flavor.”

But in the 1980s and 1990s, El Niño dumped rain across the region and the river burst into life, roaring to Mexico and flooding the desert plain. After the waters receded, the landscape had been transformed. Native cottonwood and willow trees had sprung up on the riverbanks, reclaiming space from the tough prickly salt cedar shrubs, also known as tamarisk, that had invaded the natural habitat.

“We got a glimmer of hope that a very small amount of water could make a difference,” says Pitt.

By 2005, conservation groups and academics had drawn up a plan of priorities directed at restoring parts of the delta—a blueprint they called a “Map of the Possible,” says Zamora.

The binational boundary commission (IBWC) signed on, the first recognition from governments that part of the river’s flow should be allocated to environmental uses.

But following that road map meant finding additional water for the delta, and there was none. Pressure is rising on the river, which now provides water for almost 40 million people and 4 million acres of farmland. The concern has grown even more intense as a drought that began with this century endures. Water authorities on the United States side of the river have been seeking ways to squeeze every last drop of water out of the Colorado.

For years, none of that mattered to Mexico, which is guaranteed 1.5 million acre-feet (1.85 billion cubic meters) of Colorado River water every year under a 1944 treaty that allocates every drop of the river (and more, since the treaty overestimated the river’s flow). But the United States, watching water levels fall in the main reservoirs in Arizona and Nevada, wanted Mexico to accept a reduction in its share if shortages loomed. At the same time, environmental groups on both sides of the border had begun lobbying for action aimed at restoring parts of the delta.

The Environmental Defense Fund, the Sonoran Institute and Pronatura raised money to begin their own restoration efforts, which included buying water rights from local farmers.

They tore up the salt cedar bushes and planted willow, cottonwood and mesquite seedlings on riverbank land, nurturing them with water diverted from the fields.

But the environmental groups needed more. They wanted governmental action. Mexico agreed to enter into negotiations about shortages, but insisted that the talks include conservation plans for the delta as a key point, says Zamora. Conservation organizations joined the negotiations.

“Crises are the best opportunities to get something done,” says the IBWC’s Bernal. “It is a good time to feel optimistic.”

The result, produced in 2012, was Minute 319, a five-year, U.S.-Mexican water management agreement that provides for new, jointly sponsored flows into the delta. It also calls on conservation groups to generate the base flow amounting to 52,000 acre-feet (65 million cubic meters) until 2017, using the water rights they have been buying from farmers.

Mexico’s portion of the pulse flow came from water it has banked in the United States—in Lake Mead, behind the Hoover Dam—since a 2010 earthquake damaged irrigation channels and pipelines located on its side of the border, halting planting in parts of the Mexicali Valley and thus reducing Mexico’s water needs.

The United States contribution is a commitment of $21 million to be invested in water management projects in the delta irrigation network that are intended to conserve water.

For all the tentative success of this pulse flow, new negotiations will be needed for another one after Minute 319 expires at the end of 2017. Zamora is optimistic that it will be possible, and notes that the Mexican government is supporting other efforts in the region, where agricultural runoff from the United States and treated water from Mexicali feed wetlands. “I see a lot of opportunities,” he says.

Such optimism is shared by Héctor Patiño, leader of a community-restoration group not far from the town of San Luis Río Colorado.

His perseverance is remarkable. For four years, he has been pulling up the salt cedar scrub in one of the driest areas of the region. The riverbed where he remembers swimming in as a teenager is now a flat-bottomed ditch.

But his group, with help from Pronatura and funding from the Mexican government, dug irrigation channels to bring water to this wasteland, which is wedged against the metal wall that marks the border with the United States.

With unmistakable pride, Patiño shows the willow and cottonwood shoots planted in neat rows in a small depression where the ground water is high enough to sustain them. Then he walks over a rise to another depression and lays out his plans for a lagoon.

“There was an infinity of birds,” he recalls, standing under a white-hot midday sun. “There was an infinity of fish. But it all began to disappear. Everything that was there before has gone… It will be very difficult for the Colorado River to go back to what it was before, but at least the idea is to recreate something similar so the children can see the river that I knew.”