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  • Pima County, Sonoran Institute Find Newly Occurring Fish Species in Lower Santa Cruz River

    Nov 16, 2016 | Read More News
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    File: 2016 Santa Cruz River Fish SurveyThe diversity of fish in Tucson’s “Living River” continues to grow due to improved water quality from Pima County’s upgraded wastewater treatment facilities. Initial findings from a Nov. 9 survey of conditions along the Lower Santa Cruz indicate the number and types of fish have increased and expanded along the river’s course.

    For the fourth year in a row, a team of scientists, including staff from Pima County’s Regional Flood Control District, Regional Wastewater Reclamation Department (RWRD) and Office of Sustainability and Conservation and the Sonoran Institute led the effort to determine which species currently can be found in the Santa Cruz downstream from RWRD’s Tres Rios and Agua Nueva facilities. They were joined at four locations by experts from the University of Arizona, U.S. Geological Survey, and U.S. Fish and Wildlife Service.

    Notable among the survey results is the discovery of a newly occurring species, the bluegill sunfish, at two survey sites – near the Cortaro Road Bridge and near Marana Heritage Park. Other species found at those locations include the western mosquitofish, common carp, and black bullhead catfish. The team found much less variety at two sites upstream, near the Ina Road and Camino del Cerro bridges, with only mosquitofish present at the latter location. A species detected last year, the green sunfish, were not found in this year’s count.

    “Fish are an easy visual indicator of improved river health. We are happy to see this increase in fish species along the Lower Santa Cruz,” said Claire Zugmeyer, ecologist with the Sonoran Institute. “There is a lot of variation between sites that may be related to varying flow conditions. Continued monitoring will help us understand where we have the best habitat for different species.”

    Though all species counted in the last four years have been non-native species, researchers believe is possible one or more native species wash down from upstream areas of the Santa Cruz River watershed. 

    “Previous fish surveys of the river in Santa Cruz County have found two native fish species,” said Brian Powell of Pima County’s Office of Sustainability and Conservation.  “Because native fishes can survive the types of floods that periodically occur on the Santa Cruz River and with improved river conditions documented downstream of the County’s treatment plants, we remain hopeful for their natural reestablishment. It would be a moment to celebrate.”

    The presence of so many fish in Pima County’s portion of the Santa Cruz River is almost entirely due to upgrades to the County’s two metropolitan wastewater treatment facilities, the Tres Rios Water Reclamation Facility (WRF) at Ina Road and the Agua Nueva WRF near Camino del Cerro Road. Lowering the levels of ammonia and other nutrients in the discharge as well as increasing the dissolved oxygen in the stream has improved this aquatic habitat.

    The County began operations of the expanded and upgraded Tres Rios and the new state-of-the-art Agua Nueva facilities in 2013 following the $605 million Regional Optimization Master Plan that came in substantially under budget. The Santa Cruz River downstream of the two facilities flows year-round through northwest Tucson and Marana, making it the longest stretch of river dominated by effluent in the state.


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