Delta in a Delicate Balance.

• Author: Cohn, Jeffrey P.

Public and private groups on both sides of the U.S.- Mexico border are working to restore the once lush wetlands around the Colorado River mouth and to conserve this vital water resource

Carlos Valdez-Casillas is angry and frustrated. Valdez stands atop the dredged and, in some places, barren banks of the Colorado River at the San Felipito crossing in nothwestern Mexico. He scowls as he gazes at the salt cedar, phragmites, and other exotic species sprouting where plants native to the delta had recently flourished. Here, near the Morelos Dam, some sixty miles north of the river's mouth in the Gulf of California, the Colorado wide bed attests to the ragging flood water that once gouged a route through this section of the Sonaran Desert. Todays narrow ribbon of gently flowing water symbolizes the river's drastically altered state on both sides of the nearly U.S.-Mexican border.

"If we could just be assured of even this much water every year and a flood every few years, the data would be green again," says Valdez, the former director the Center for Conservation and Use of Natural Resources at the Technology Institute of Monterrey in Guaymas, Sonora. "The river has shown a lot of patience. If we just get out of the way and] let nature do what it will do, the plants will restore themselves if the water is there."

Actually, as Valdes readily admits, the Colorado River delta has made a remarkable if incomplete comeback over the last two decades. The mason: Water has been there, at least occasionally. As a result, water once again fills many of the river's former meanders. Old oxbows, lagoons, and ponds have returned. Tall cotton-woods, stately willows, and thorny mesquites once again dot the delta. And tassel-topped cattails surround salt marshes that are home to countless nesting and migrating birds.

"This is a very important place ecologically," states Valdes, who is now with the North American Commission for Environmental Cooperation in Montreal, Canada. "Most people think of the delta as A lost and dead ecosystem. No, no, no! It is Not gone!"

Valdez should know. For the past decade, he and a team of U.S. and Mexican scientist have repeatedly hiked through, floated down, driven along, and flown over the delta and surrounding lands. They have documented a natural restoration produced by periodic El Nino flooding by the Colorado and a dam-and-water-storage system in the United States that can hold no additional water from melting snow. But, whether the delta continues to recover--and the extent of that recovery--remains to be seen. As usual when it comes to Colorado, the delta depends as much on continued above-average flows and the resolution of very complicated water issues in the United States as it does on action in Mexico.

The Colorado River flows 1,450 miles from the Rocky Mountains in Colorado southwest through the canyons of Utah and Arizona before turning south towards Mexico and the Gulf of California. The river and its tributaries drain 242,000 square miles in seven U.S. states (8.5 percent of the continental United States) plus another 2,000 square miles in Mexico. Before people started tinkering with it, the Colorado often flooded its banks in spring and early summer when runoff from melted snow and rainstorms turned the river into a raging giant. The floods swept away salts and sediment, and scoured cottonwood seeds, a prerequisite for their germination. As summer wore into fall, the river gradually shrank, in some years to a mere trickle.

As the Colorado neared the gulf, the river slowed down and spread out, dropping its load of sediment. The river formed a large delta that once covered almost two million acres, an area the size of Rhode Island. The delta was fed by nutrients carried by the river, especially during floods, and by high tides in the gulf that extended coastal estuaries more than thirty miles inland. The result was an unusually rich riparian and wetland oasis in the middle of the Sonoran Desert. Where the river now separates the Mexican states of Sonora and Baja California, early explorers reported large numbers of coyotes, deer, javelina, beaver, geese, and ducks. Fish and shrimp abounded in the gulf and spawned in the delta. Perhaps as many as four hundred vascular plants once grew there.

"The still waters of a deep and emerald hue, colored by algae, I suppose, but no less green for all that," wrote American naturalist Aldo...