Photos: Researchers release tiny fish into Tucson's Santa Cruz River

Carrying frame backpacks laden with water-filled buckets, Michael Bogan and Besty Grube worked their way along the bottom of the Santa Cruz River on Wednesday morning and settled on a spot just south of the bridge that carries West Starr Pass Boulevard over the once-dry stream bed.

Bogan, an assistant professor at the University of Arizona, along with Grube, a top minnow and pup fish specialist with Arizona Game and Fish, shouldered their loads along the sandy river bottom to where a wandering strip of greenery marks the presence of water.

In each bucket were 50 longfin dace, a tiny fish about 2.5 inches long. The diminutive fish, roughly spindle-shaped and a mottled gray-brown, will re-stock what's known as the Heritage Reach — a one-mile section of the Santa Cruz River near Downtown Tucson — that's part of larger-scale effort to restoring the river's ecology.

The effort is part of  collaborative effort between the Pima County Office of Sustainability and Conservation, the Pima County Regional Flood Control District, the Arizona Game and Fish Department, U.S. Fish & Wildlife Service, the city of Tucson and the University of Arizona. Along with the Heritage Reach, nearly 500 fish were stocked downstream of the county's Agua Nueva Water Reclamation Facility, near West El Camino Del Cerro and North Silverbell Road.

"This is the first time they've been here in a 100 years," said Bogan, as he used his cellphone to video the fish as some began to swim hard, rushing upstream toward shade formed by a cluster of Veronica weeds.

“Before it disappeared because of a lack of water, invasive species, and other factors, the longfin dace historically made their home in the Santa Cruz River,” said Ian Murray, a conservation biologist with the Pima County Office of Sustainability and Conservation.

More than a century ago, the section of river on the edge of Downtown was a perennial water source, but throughout the 20th century, water became increasingly rare through the Heritage Reach as the city piped water to homes and agriculture projects. For much of the last decades, the river bed is parched until monsoon rains send thousands of gallons of water ripping along its banks.

"This was a perennial water source, but that dried up around 1913 or 1914, and so all the fish species, including the dace, disappeared," said Bogan. The fish remained in waters in the mountains and near Santa Cruz County, he said, but in the Heritage Reach, the lack of water meant the loss of the species.

However, in 2019, city and county leaders began releasing reclaimed water as part of the Santa Cruz River Heritage Project. In October 2020, Arizona Game and Fish led a team of biologists to capture hundreds of top minnow from the Santa Cruz River in Tubac, and release them into the Heritage Reach. Unlike the top minnow, the longfin dace is not considered threatened or listed as an endangered species, however, it is covered by Pima County’s Multi-Species Conservation Plan, county officials said.

The dace were captured by researchers in the county's Ciénaga Creek Nature Preserve out past Vail and brought 25 miles to the Heritage Reach.

Murray said that the reintroduction of the dace is a major step toward restoring the river’s native fish fauna.

"Restoring this native species supports the MSCP and the Sonoran Desert Conservation Plan’s goals of keeping our biodiversity extant,” he said.

"Now that we have water in the river back in downtown, we've got stable habit and good habitat," said Bogan, as he stood along the bank of the river, as a few people excitedly pointed out longfins racing in the cool water.

While dace are common in the state, they're disappearing as watershed dry up, Bogan said, and he likened the effort to bring the fish to Downtown Tucson as a kind of ecological "bank" to preserve the species, and prevent them from becoming endangered.

"And for Tucsonans, this is bringing life that was here back to river, and that disappeared because of the city's growth in the first place," he said.

"We owe it to the species to give them a chance and bring them back here," Bogan said.