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  • Wastewater improvements permit return of endangered fish to Lower Santa Cruz River

    Dec 14, 2017 | Read More News
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    File: Gila topminnowImproved water quality in the Lower Santa Cruz River resulting from upgrades to Pima County’s wastewater treatment facilities have allowed the return of a native species of fish to the Tucson area for the first time in more than 70 years.

    Fish surveys conducted in November confirmed the presence of the Gila topminnow, an endangered species. Previous annual fish counts of the Santa Cruz had detected only non-native fish species in the Tucson section of the river.

    The fish surveys were conducted by Pima County and partner organizations including the Sonoran Institute, U.S. Fish and Wildlife Service, Arizona Game and Fish Department, University of Arizona, and U. S. Geological Survey Arizona Cooperative Fish and Wildlife Research Unit. The surveys took place at four sites along the river, from near Silverbell Park in the south to Marana Heritage River Park in the north. The main focus of the surveys was to determine the species living in the river and their relative abundance.

    “It is extremely gratifying to see the topminnow return to a stretch of the river where they haven’t been seen for decades” said Brian Powell of Pima County’s Office of Sustainability and Conservation. “They used to be one of the most-common native fish in Southern and Central Arizona. However, after the turn of the 20th Century, population growth, groundwater pumping and competition from non-native fish like the mosquitofish pushed them to near extinction. For many years, the only significant population in this part of the Gila River Watershed existed in Upper Sonoita Creek and parts of northern Sonora, Mexico.”

    While this is the first time a native fish has been found in this stretch of the river, the number and variety of species has been increasing in recent years. This is due almost entirely to upgrades to Pima County’s two metropolitan wastewater treatment facilities that now produce exceptionally clean effluent. These facilities then discharge this treated effluent to the Santa Cruz River. The County began operations of the expanded and upgraded Tres Rios Water Reclamation Facility (WRF) at Ina Road and the new state-of-the-art Agua Nueva WRF near Camino del Cerro Road in 2013.

    In addition to the improved the aquatic habitat as a result of higher-quality water leaving the facilities, the improvements have increased the amount of water naturally recharging the local aquifer. Gone too are the terrible odors that once emanated from the treatment of wastewater. These improvements, along with investments in infrastructure and recreation opportunities such as The Loop multi-use path, have made it easier and more enjoyable for residents to discover the flowing Santa Cruz River.

    Evan Canfield, the Regional Flood Control District’s Project Manager on the Living River Project, which tracks conditions in the Santa Cruz, considers the Gila topminnow’s return a validation of Pima County’s efforts to restore the river to a more natural, functional state.

    “In a very real way, the return of the topminnow is emblematic of the improving river conditions,” Canfield said. “In our first fish survey for the Living River Project four years ago, we found almost no fish in this part of the Santa Cruz. Today the river supports a population of endangered fish. This shows we’re moving in the right direction.”

    The RFCD has begun an updated management plan for the Santa Cruz to recognize that the river is an increasingly valued community resource and attraction that also needs to be managed to safeguard property and ensure public safety.

    The presence of an endangered species in the Santa Cruz River will not impact County operations along the river because of the County’s Section 10 permit issued by the U.S. Fish and Wildlife Service. The County anticipated and planned for the possible establishment of topminnow and other federally protected species to the river, as well as impacts to them from activities covered in the permit.