The Gila topminnow, an endangered species of fish not seen in Southern Arizona's Santa Cruz River in a decade, was found in the river last month, the Arizona Game and Fish Department announced this week.
The species' return demonstrates that an effort to clean up the polluted river is working, the department said, citing a 2009 upgrade to the Nogales International Wastewater Treatment Plant, which empties treated wastewater into the river, as the key factor in the waterway's recovery.
A U.S. Fish and Wildlife Service biologist said the topminnows were living upstream from the river and likely were washed into the river by a flood. Now, he added, state and federal agencies and nonprofit organizations must work to ensure the species survives and thrives in the river.
Claire Zugmeyer, an ecologist at the Tucson-based Sonoran Institute, said properly treated wastewater is "a key solution for keeping desert rivers alive." We told you about Zugmeyer's and the Sonoran Institute's work to aid the river's comeback in Cruz Control, a story in the November 2015 issue of Arizona Highways.