A Promising Future for This River, Thanks to… Sewage Water!

Once the most endangered river in the United States, Arizona’s Santa Cruz River has been reborn in recent years by reintroducing treated wastewater. Thus, it has restored threatened ecosystems and welcomed back some 150 species, including plenty of insects.

“I think the biggest surprise in our study was just how quickly species returned to the Santa Cruz River when the flow was restored — it was astounding how fast biodiversity could recover when given a chance,” explained co-author Michael Bogan, a professor of aquatic ecology at the University of Arizona. “That stretch of the Santa Cruz River had lost year-round flow due to groundwater pumping more than 100 years earlier — and yet within weeks of flow being restored, there were literally dozens of aquatic species living in the reborn river.”

Indigenous populations sustainably used the Santa Cruz River for thousands of years, which runs 290 kilometres through Arizona and Mexico. Before the 1900s, the river flowed year-round. However, due to climate change, irresponsible wastewater disposal, and groundwater pumping, the river became a dry wash – a body of water that fills up momentarily after heavy rains but otherwise remains dry. Scientists reintroduced effluent, sewage discharged from an industrial plant with disease and pollutants first removed. Pima County invested $600 million to upgrade two wastewater treatment plants in the Tucson area. After two years, populations of hundreds of invertebrate species, fish, toads, and turtles, rebounded. “This is a rare ‘good news’ story in ecology and wildlife, where human development is helping to restore an ecosystem.”