“The treatment wetland has been one of the great success stories in the Colorado River Delta region.”Osvel Hinojosa, National Geographic Explorer/Director del Programa de Agua y Humedales, Pronatura Noroeste
It has turned desert into oasis, a noxious pollutant into a source of new life. Our Colorado River Delta program is filled with amazing outcomes, and the Las Arenitas treatment wetland is a truly remarkable story of reclamation and renewal.
Flying over this area of the Delta, just south of the U.S./Mexico border and past Mexicali, the capital of Baja California, you would never guess that you are looking at what used to be one of North America’s most important wetlands. Before upstream dams and diversions for farms and cities in the U.S. and Mexico slowed the Colorado River to a trickle, the river fed almost 2 million acres of fertile habitat for birds, fish, and other wildlife. Now, you see a panorama of tan, the color of dry. The dusty nothingness is so absolute that it’s no wonder most people had until recently given up the Delta for dead.
But soon you’ll see another sight, our vision of what is possible in this desiccated landscape. Next to a municipal wastewater treatment plant in the middle of this desert appears an unlikely expanse of water, vegetation, birds, and even tourists—250 acres of life.
Raising a Stink
All of this bounty started as waste. In 2007, to help deal with wastewater from its growing metropolitan region, the Mexicali state water authority, through the Comision Estatal de Servicios Publicos de Mexicali (CESPM), built the Las Arenitas Wastewater Treatment Plant. Soon after it began operation, however, it was apparent that the plant was already over capacity. Wastewater that was not treated up to standards suitable for human contact flowed into the Hardy River, a tributary of the Colorado River that is popular for hunting, fishing, boating, and swimming. Owners of homes and vacation camps along the river objected not only to the smell, but also to the risks to their health, their property values, and their tourist and recreation businesses.
Amid this mess, Francisco Zamora Arroyo, director of our Colorado River Delta Legacy Program, saw both a solution and an opportunity. “In 2008, we approached CESPM with a plan to create a wetland next to the treatment plant that would provide additional treatment capacity, while also enhancing the river system and the local economy,” he says.
The idea was the wetland would acts as a biofilter, removing sediment and pollutants from the partially treated wastewater. Natural chemical processes and microorganisms living in the wetland’s vegetation would break down organic materials over time and improve the water quality.
We began construction in 2009. The treatment wetland is now 70 percent completed—and it’s working. The wetland is helping the state water authority and the city of Mexicali meet water quality standards at a lower cost than expanding the plant itself, and the improved conditions of the Hardy River are boosting property values and tourism and recreation businesses in the area.
But that’s just the start. The Delta is a critical stopover point for birds traveling along “Pacific Flyway,” the major north-south migration route that extends from Alaska to Patagonia at the southern tip of Argentina. The wetland has created new habitat for these birds, and provides a unique opportunity for people living in Mexicali to experience a wetland 20 minutes outside the city. For now, the recreation area includes walking trails and a small visitor center, but the state has proposed creating a more extensive municipal park in the future.
Furthermore, thanks to a forward-looking agreement that Sonoran Institute and our partner Pronatura Noroeste reached with the state government and CESPM, the wetland’s benefits extend far beyond the treatment area itself. We asked that 30 percent of the treated “effluent” (wastewater) be dedicated to the Hardy River. This ensures that, at current capacity, some 8,000 acre-feet of water flows into the Hardy River, and eventually into the Colorado River, every year for the next 20 years. The dedicated amount increases as more wastewater is treated at Las Arenitas, and will probably ultimately rise to about 12,000 acre-feet. The agreement represents one of the only instances in Mexico that effluent has been dedicated to environmental purposes. (story continues below sideshow)