By JESSICA KONG
Arizona Sonora News
Experts say there’s been a noticeably improved environment for the fish community along the 23-mile stretch of the Santa Cruz River ever since Pima County’s wastewater treatment facilities, the Tres Rios Water Reclamation Facility (WRF) and the Agua Nueva, were upgraded in 2013.
The Sonoran Institute, joined by Pima County, has been working with the Arizona Game and Fish Department, the University of Arizona, the U.S. Geological Survey and the U. S. Fish and Wildlife Service to conduct an annual fish survey.
The Living River series developed by the Sonora Institute and the county reports on the river. The Sonoran Institute evaluated the wildlife conditions of water, air, and energy.
The survey team examined three stretches of the river beginning at Marana Flats, Cortaro Narrows, and leading down south to the Three Rivers. On one day, the results were collected on about a 100-meter stretch in each site near Marana Heritage Park, Cortaro Road, south of Ina Road, and south of Camino Del Cerro.
Efforts from Pima County’s Regional Flood Control District, Regional Wastewater Reclamation Department, and Office of Sustainability and Conservation have contributed to maintaining the livelihood of the river’s ecosystem.
Claire Zugmeyer, an ecologist from the Sonoran Institute, found non-native fish in this year’s survey, namely Western Mosquitofish, Black Bullhead, Common Carp, and Bluegill Sunfish. Compared to the 2015 Living River water report, the Green Sunfish was replaced by the Bluegill while the rest remained the same from last year. Native fish such as the endangered Gila Topminnow still live upstream, but they’re less commonly found.
In addition to the Topminnow, the Gila Chub, Desert Sucker, Sonora Sucker, and Longfin Dace were native fish species that once swam in the Santa Cruz River before the river’s decreased flow in recent years.
“We’re hopeful that they can come back. It might just be a waiting game. And right now, we just have these non-native species and we’re not too sure how they’re getting into the river,” Zugmeyer said.
“But likely, people are fishing in the nearby lakes like the lake at Columbus Park. There’s a lake with fish there and people might be releasing fish that they caught into the river.”
According to the 2015 Living River report, the decreased flow of the river is likely due to an influx of infiltration since the updated water treatment facilities.
“Reductions in effluent released from Agua Nueva also contributed to changes observed in the Three Rivers reach. Some wastewater was redirected to the Tres Rios and thus released further downstream, and more effluent was used to supply recharge basins near Agua Nueva,” the report said.
The Santa Cruz River has sustained wildlife for over 12,000 years, and supported neighborhood communities with accessible water.
Sampling is one method in determining the water quality of the river. However, the fish effectively help indicate the river’s health for researchers in the future.
Brian Powell, the program manager from Pima County’s Office of Sustainability and Conservation, observed from the fish survey the positive changes of decreased turbidity and suspended solids found in the water.
“For turbidity, the cloudiness of the water has gone way down so it looks quite clear, and that’s excellent. The suspended solids you can’t see, but those are like salts in the water. Those have gone down as well,” he said.
According to the 2015 Living River report, “nitrogen and other nutrients enter the river from air pollution, fertilizer, surface runoff, and release of effluent. While elevated nutrient levels can benefit growth of riparian plants, they can also lead to poor conditions for aquatic wildlife.” This year, the fish survey concluded that as dissolved oxygen has increased, ammonium and biochemical oxygen demand (BOD) have decreased.
Essentially, the increase of dissolved oxygen indicates a better survival of aquatic plants and life while a decrease in ammonium and BOD lessens the susceptibility of fish fatalities.
“Some of the bigger measures are ammonium. So ammonia is toxic at high levels. And that’s probably one of the reasons why we’re seeing an increase in diversity of fish,” Powell said. “That’s probably why we’re seeing an improvement in the macroinvertebrate community. So ammonia has gone down dramatically.”
James DuBois, a hydrologist from Pima County’s Regional Wastewater Reclamation Department, would like to see more fish diversity and a healthy recovery of the aquatic habitat along the Santa Cruz River. The Sonoran Institute and Pima County are anticipating for native fishes to migrate back along the river in the future.
“There are points upstream in the watershed where native fish exist along the treatments in Santa Cruz,” DuBois said. “And if we get a storm of them so that they can wash those fish into our environment, hopefully they will be able to compete with some of those non-native species and proliferate in the streams too.”
Download high resolution images here.
Jessica Kong is a senior majoring in journalism at the University of Arizona and she plans to pursue graduate school in business after college. Born and raised in Phoenix, she enjoys traveling, hiking, working out, binge watching movies and constantly wishing she had a dog (maybe one day).