German Munoz looked out at the river before him and talked about the days when dolphins swam here, 60 miles from the sea. “The wave made noise like a train,” he said, describing the tides that would roll up the Colorado River from the Gulf of California and then a mile or so up this tributary, past his family’s land.

“There would be all kinds of fishes jumping, very happy. And then, the dolphins would come, chasing the fishes.” That was in the 1950s, when the Colorado still flowed regularly to the gulf — as it had for tens of thousands of years, washing sand and silt down from the Rocky Mountains to form a vast and fertile delta. In the last half-century, thanks to dams that throttled the Colorado and diverted its water to fuel the rise of the American West, the river has effectively ended at the Mexican border.

The Colorado delta, once a lush network of freshwater and marine wetlands and meandering river channels and a haven for fishes, migrating birds and other wildlife, is largely a parched wasteland. Munoz last saw a dolphin as a teenager in 1963, the year the last of the big Colorado dams, the Glen Canyon, began impounding water 700 miles upstream.

“The river doesn’t come here anymore,” he said. But after decades of dismay in Mexico over the state of the delta, there is reason for some optimism. An amendment to a seven-decades-old treaty between the United States and Mexico, called ‘Minute 319’, will send water down the river once again and support efforts to restore native habitat and attract local and migratory wildlife.

Water sharing

Water for the environment is only one part of ‘Minute 319’, which also calls for more water-sharing between the two countries and the amounts for the delta are a trickle compared with the huge volumes siphoned off for cities, farms and industries. But, a regular base flow of even a small amount of water should breathe new life into the riparian corridor, the river’s main channel.

The amendment, which is into effect for five years, also calls for a larger one-time release of water that will mimic the once common floods that rejuvenated the delta every spring, scouring out sediment and old vegetation and opening up areas for new vegetation to thrive.

During this pulse flow, the Colorado should once again reach the sea. “The new agreement will definitely help to restore the Colorado,” said Efrain Nieblas, director of the environmental protection agency for the state of Baja California.

In the tidal estuary at the northern end of the gulf, the influx of fresher water will reduce salinity, aiding members of the indigenous Cucapa community and others who fish for gulf corvina and shrimp. “It’s really important to connect the river with the ocean,” Nieblas said. The delta will never be like it was before the dams — for one thing, much of the riparian corridor is now hemmed in by irrigated farmland and Munoz surely will not see dolphins frolicking past his door again.

“We’d been working hard for many years to have something like this,” said Francisco Zamora, director of delta projects at the Sonoran Institute, which is based in Tucson. “We know it works. You add a little bit of water, and the trees will grow.” For any amount of restoration work to succeed, water is a necessity. Colorado River water is a precious commodity — most years, every drop is spoken for.

About 90 per cent of the river’s annual flow of roughly five trillion gallons goes to California, Arizona and the five other Western states in the Colorado basin.

Over the years, these states have argued over how the water is shared and they will no doubt fight more as climate change and population growth put pressure on already overtaxed supplies.

But, Mexico has largely been an onlooker during such squabbles; under the 1944 treaty, it is guaranteed about 500 billion gallons a year. That water reaches the border at Morelos Dam, the last on the river, where it takes a sharp right turn into canals for delivery to Mexican farms and cities for drinking water.

Unless heavy winter snows in the Rockies lead to higher spring flows than the upstream reservoirs and canals can handle which last happened to any significant degree 15 years ago, no water goes through the dam and down the riparian corridor.

But that does not mean there is no water to be found. There is Colorado water in parts of the delta; it just gets there in roundabout ways. But for more areas to be restored, more water is needed and it must come down the corridor. The river must flow. As part of the agreement, the conservation groups pledged to provide the water for the base flow, roughly 3.5 billion gallons a year, by buying unused water rights from the Mexican farmers.

They have already acquired about 40 per cent of that amount, although as Zamora noted, ideally the base flow would be closer to 20 billion gallons a year. The water will be used to irrigate plantings and to raise the water table along the corridor to enable the water-hungry cottonwoods and willows to survive.The pulse flow about 35 billion gallons, to be released over one or two months by spring 2016 at the latest, will be provided by Mexico.

Saving water

The idea is not to cut amounts currently being used by farms and cities, said Francisco Bernal, director of the Mexicali office of the International Boundary and Water Commission, the binational organisation that administers the 1944 treaty, but to save water through conservation improvements, some of which under ‘Minute 319’ will be paid for by water districts in the United States in return for some of Mexico’s water. Those improvements include lining canals so less water seeps through.

“We want to conserve enough water to share with the environment,” Bernal said. Scientists are also trying to better understand hydrologic conditions in the delta so that the pulse flow will be effective. Jorge Ramirez, a hydrologist at the University of Baja California, said that in some areas along the corridor the water table is very low because so much water has been pumped out for agriculture. If the pulse water is released too slowly, much of it may be absorbed in these dry areas and no water may reach the gulf. “This is the key — how fast we’re going to put in the water, in order to have the water flowing down the whole river and into the estuary,” Ramirez said.