A small native fish is swimming in the Santa Cruz River in Tucson for the first time in more than a century.
Roughly 600 longfin dace, each no more than about 3 inches long, were set free Wednesday at two locations along the rejuvenated river, where Pima County and Tucson are using treated wastewater to restore natural habitat killed off by human development in the early 20th century.
“It’s bringing some of the life back to the river that was here that disappeared because of the city’s growth in the first place,” said University of Arizona aquatic ecologist Michael Bogan, who has been monitoring the river restoration. “Personally I feel like we owe it to the species to give them a chance and bring them back down here.”
Longfin dace are swimming in Tucson's Santa Cruz River again after being gone for more than 100 years.
Bogan said the dace disappeared — along with all the other native fish — in about 1913, when irrigation diversions and groundwater pumping caused the once-perennial Santa Cruz to run dry through Tucson.
The fish managed to hang on in some irrigation ditches and upstream tributaries, he said, “but they were gone from the river here.”
The energetic, olive-green minnows made their triumphant return to the Santa Cruz in large Coleman coolers stamped with the words “Fish Transport,” after being scooped from Cienega Creek near Vail, about 25 miles away.
It took the team about 90 minutes to net all 600 dace from the creek’s much larger population of the fish, said Arizona Game and Fish Department biologist Besty Grube.
“We got some chunky ones,” Bogan said, as the transplants were transferred into a pair of 4-gallon buckets strapped to backpacks to be carried down to the river.
Wednesday’s release was part of a cooperative effort by the county, the city, the UA, Arizona Game and Fish and the U.S. Fish & Wildlife Service.
Only one dace died during the operation. The rest quickly settled into their new home.
Experts hope to see them start spawning later this spring.
“The fish seemed pretty vigorous and they swam off,” said Ian Murray, a conservation biologist with the Pima County Office of Sustainability and Conservation. “They’re pretty tough fish.”
About 500 of the dace went back into the river just downstream from the county’s Agua Nueva Water Reclamation Facility, near El Camino Del Cerro and Interstate 10. The rest were set free just south of the Starr Pass Boulevard bridge, where the city began releasing recycled sewer water in 2019 as part of its Santa Cruz River Heritage Project.
That northerly flow has created a narrow, mile-long ribbon of green that reaches to Congress Street and beyond, depending on the day.
The dace joins an even smaller native fish known as the Gila topminnow, which was reintroduced to the downtown stretch of the Santa Cruz in October of 2020.
The topminnow has been on the endangered species list since 1967, but it’s doing quite well along the rewatered river. Grube said the transplanted population of around 500 tiny topminnows has grown to roughly 2,000 over the past 18 months or so.
Topminnows and longfin dace could be seen swimming side by side within moments of Wednesday’s release.
Grube said the two species will compete with each other to an extent — and the much-larger dace might occasionally harass their smaller neighbors — but ultimately she expects them to coexist downtown just as they do in Cienega Creek.
The longfin dace isn’t threatened or endangered, and Bogan said releases like this one could help keep it that way, as populations elsewhere in Arizona come under threat from climate change, drought and water pumping.
The idea is to prevent the species from becoming endangered by “putting it into as many habitats as possible,” he said.
The little fish also have a part to play in the larger river ecosystem.
“They do things like eat mosquito larvae,” Bogan said. “And they’re food for birds, so we’re hoping soon to see things like kingfishers and herons down here eating some of the dace that we’ve reintroduced.”
