They are only one or two inches long, but their mere presence is immense. The federally endangered Gila topminnow had not been seen in its native habitat, the Santa Cruz River watershed, for more than a decade. Then, in December 2015, what we all hoped for happened: they came back. Their numbers were small at first, but the annual fish survey one year later showed their population was not only established, but growing.

Decades of pumping surface and ground water out of the Santa Cruz had dried up long stretches of the river. The sections that flow year-round relied on polluted wastewater that killed off the topminnow and many other living things. Federal Clean Water Act requirements, along with unrelenting pressure from conservation organizations, eventually led to treatment plant upgrades. The Sonoran Institute has helped validate that the cleaner wastewater, or “effluent,” has begun reviving the river’s natural habitat, and the topminnow’s return is a conservation triumph. It signals that years of effort to bring the Santa Cruz River system back from the brink are succeeding, and shows how remarkably resilient nature is if given a chance.

Ironically, the success of effluent also spells trouble. As a resource, effluent has become as coveted as the fresh water it replaced. There’s growing demand to take effluent out of the river for human use, something that would threaten to undo the hard-won environmental gains.

This is a story of second chances, of a little speckled fish that came back from the brink to survive in its native waters, of a habitat that humans ruined and then restored, and of a once-toxic waste now being used to sustain life. As a society, we’ve made so much progress in learning the importance of keeping water in the river. Are we really willing to repeat the mistakes of the past?

From its headwaters in the San Rafael Valley in Arizona to its confluence with the Gila River north of Tucson, the Santa Cruz River stretches over 200 miles and is the only river to cross the U.S./Mexico border twice. It first flows south from its headwaters into Mexico, where it completes a 25-mile U-turn and flows back north into the United States (a stretch referred to as the “Upper Santa Cruz”), then through Tucson (the “Lower Santa Cruz”), and eventually into the Gila River, a tributary of the Colorado River.

Like all rivers, the Santa Cruz is much more than its water. “The river system provides many important benefits to nature and our community,” says Claire Zugmeyer, the Sonoran Institute’s ecologist. “The vegetation it supports improves air quality, helps control flooding and erosion, filters groundwater, provides important wildlife habitat, and offers respite and spiritual renewal for people.”

The river has been providing life-sustaining water to humans for more than 12,000 years. Unfortunately, over the last century, human demand for water has taken a devastating toll on the Santa Cruz. Surface water and groundwater have been pumped for drinking water, agricultural irrigation, and to fuel industry and commerce—to such an extent that much of the river has gone dry. Sections that do have year-round water are flowing because of wastewater inputs that until fairly recently were toxic to the river environment. A mass die-off of cottonwoods on an 8-mile stretch of the river in 2005 was a huge wake-up call. If the river stayed in such bad shape, the corridor of life it supported could be lost.

In 2008, numerous research and monitoring efforts were taking place to understand the health of the river and to demonstrate how healthy rivers benefit people. The Sonoran Institute joined the effort when it became apparent we could play a critical role in synthesizing data being collected by multiple partners and create a report to that would provide a much clearer picture of the river’s condition and needs.

“Given the importance of the river and the complexities of an effluent-dominated river, we wanted to see what we could learn by tracking changes in specific indicators—like water quality—on a year-to-year basis,” says Zugmeyer. “Understanding which elements are changing and how those changes might affect the ability of the river to properly function allows us to be direct in our stewardship efforts.”

To determine which indicators to track, we convened a science advisory committee of ecology, wildlife, and hydrology experts to bring the best available science to guide our Living River health assessments.

“Sonoran Institute brought this great panel of academic people and agency people and our group to try to work out not only what the data might mean, but what data is important,” says Sherry Sass, president and one of the founders of Friends of the Santa Cruz River (FOSCR). FOSCR is a non-profit group of volunteers that since 1991 has been advocating for keeping water flowing in the river for the benefit of the river environment and for people. “What do we want from the river? What are we looking at? There are value judgements in there, and those are tricky. Sonoran Institute did just an unbelievable job sorting out what, bottom line, is important in terms of this river’s survival—to us who live along it and to the broader riparian-concerned community.”

“What do we want from the river? What are we looking at? There are value judgements in there, and those are tricky. Sonoran Institute did just an unbelievable job sorting out what, bottom line, is important in terms of this river’s survival—to us who live along it and to the broader riparian-concerned community.”
–Sherry Sass, Friends of the Santa Cruz River

The result of this collaboration was the first Living River report, which began with a baseline study to assess conditions in a 20-mile stretch of the river from Rio Rico to Amado in Santa Cruz County, Arizona, from October 1, 2007-September 30, 2008. These measurements were taken before completion of upgrades to the Nogales International Wastewater Treatment Plant (NIWTP) in Rio Rico, and conditions were pretty grim.

“Poor water quality made it really challenging for fish and other aquatic wildlife. People couldn’t swim in the water because E.coli levels were elevated. We found a total of two fish in the river. Not two species of fish. I am mean two TOTAL fish!” says Zugmeyer. The two fish were native Longfin Dace. The federally endangered Gila topminnow were nowhere to be found.

Poor water quality was also having an effect on riparian vegetation. High nitrogen levels had created a thick layer of algae on the bottom of the stream channel in some areas, preventing water from filtering down into the aquifer. As a result, the groundwater table in those areas had lowered out of reach for the roots of plants and trees. University of Arizona scientists found that this was the likely cause of the 2005 cottonwood die off.

Bottom line: The river was stressed. And so were the people who cared about it. On the heels of the research effort into the tree die-off, we began coordinating an event where groups doing work on the river can come together for two days a year to share ideas and experiences. The first annual Santa Cruz River Research Days gathering was held in 2008. It has become a valuable forum for those interested in conservation efforts, both of the river’s natural and cultural resources.

“The Sonoran Institute is the lynchpin,” says Sherry Sass. “They provide the continuity that so often volunteer groups can’t. They are a steady presence and can do these long-term things that are of tremendous benefit not just to groups like ours but to the river itself. They are a professional champion.”

Understanding the Importance of Effluent

Back in 2009, there was still a lot of uncertainty about the benefits of effluent, and our 2009 baseline assessment showed why. In the next year, however, after years of activism by the FOSCR and others, the NIWTP in Rio Rico completed significant upgrades that reduced levels of nitrogen and other organic compounds in the effluent flowing into the Santa Cruz. Results of subsequent Living River assessments showed a river starting to recover. A year after the treatment plant upgrades, the number of fish counted rose from 2 to 142, and annual fish counts have tallied several hundred since then.

Male and female Gila topminnow. Image courtesy of AZGFD/Bruce D. Taubert

While increasing fish numbers are a good indicator of a healthier river, other signs aren’t so easy to read. The river isn’t flowing as far in some spots as it used to, for example, probably because of better infiltration into the water table as a result of the reduced nitrogen levels. E. coli levels still exceed healthy levels after the upgrade, indicating other potential sources of contamination, such as from livestock near the river. Lack of rain and flooding also affect conditions from year to year. The system is complex, which makes our Living River work even more important.

“Our group is made up mostly of biologists and scientists, and we’re very involved in data gathering, but we’re not great data interpreters,” says Sherry Sass. “We just don’t have the time, energy, or expertise to do it. That’s where the Sonoran Institute is so helpful. They have done a fabulous job. They have a huge database, and they’ve set up the Living River publications to be most useful in actual protection of the resource—and that’s hard to achieve.”

This success didn’t go unnoticed. The Living River reports for the Upper Santa Cruz caught the attention of Pima County, Arizona, which had undertaken its largest public works project ever, investing $600 million to upgrade two wastewater treatment plants on the Lower Santa Cruz, in the Tucson area.

“We saw the success of the Upper River Santa Cruz work and wanted a way to educate the public, stakeholders, and decision makers about Pima County’s community investment and the improvements taking place at our Tres Rios and Agua Nueva reclamation plants,” says Evan Canfield of the Pima County Flood Control District.

Together with Pima County, the Sonoran Institute since 2013 has been compiling Living River reports on the Lower Santa Cruz River, a 23-mile stretch northwest of Tucson. Modeled on those for the Upper Santa Cruz, these reports began with baseline measurements of conditions prior to the treatment facility upgrades, and have continued with annual assessments, tracking water quality, native fish, wildlife, and the overall ability of the public to enjoy the river.

“The Living River reports simplify a massive amount of information about the river down to the most salient elements and present it in a way that is engaging and understandable to anyone, from government officials needing to make management decisions to children using it in their classroom,” Canfield says. Two education programs, the Living River of Words for students K-12 and Living River Academy for teachers, use the Living River reports as guides.

Canfield explains that these reports look holistically at the river—not just considering the sediment or geometry or vegetation or fish—but also the human interaction. “That’s been extremely important, because it allows us to talk about the river as a resource and an asset. Without a report like this which weighs out the case for the Santa Cruz River as an amenity for the community, elected officials may not make choices that support that amenity. As a community, we need to decide where our water resources are going to go. The Living River reports show that water in the Santa Cruz River is undoubtedly a valuable resource.”

Like those from the Upper Santa Cruz, the reports have shown improvements to river conditions from better-quality effluent. The water is clearer, there are four fish species living in the river (three more than in previous years), and people can enjoy walking or biking on the Loop recreation trail along the river in Tucson without the dreaded rotten egg smell.

“You certainly hear people who live along the river sounding much happier,” Canfield says. “They are very excited about the Living River project. They’re sending teachers to Living River Academy. It’s a 180-degree about face from feeling the river is a detriment to their neighborhood to seeing it is an asset. They talk about taking walks along the river and want to do economic development and revitalization in the areas nearby.”

A Vision of What We Have Gained, And What We Could Lose

Nowhere is the Santa Cruz River’s history and cultural significance more visible than at the Tumacácori National Historical Park. Encompassing three 18th century mission sites near the U.S./Mexico border—Tumacácori, Guevavi, and Calabazas—the park celebrates the history of the native O’odham people, missionaries, settlers, soldiers, and others who spent time there, all because of the water in the Santa Cruz River. In 2002, the park’s boundary was expanded, and now includes a one-mile stretch of the Santa Cruz River.

“The river was the lifeblood of the various communities living here,” says Bob Love, park superintendent. “The mission was here because the Native American community was here, and they were here because of the river and its water.”

Thanks to the effluent that flows out of the nearby Nogales International Wastewater Treatment Plant, the Santa Cruz River in this stretch has surface-flowing water for most of the year, supporting an abundant diversity of plants and animals, including a cottonwood-willow forest, one of the rarest forest types in North America. It provides habitat for mountain lions, coyote, bobcat, deer, coatimundi, and javelina. It is also part of what Audubon Arizona has named an “Important Bird Area” for the density and diversity of birds it supports, including nesting Yellow-billed cuckoos, a species of conservation concern. All of this life has made the park and connecting Juan Bautista de Anza Trail, the two publicly accessible parts of the river in this area, increasingly popular with hikers, equestrians, and birders.

“It’s an amazing natural resource to have,” Love says, “and it wouldn’t happen if not for effluent.”

Tumacácori’s mile of river is also one of the sites of the Gila topminnows’ comeback. For all the people who fought so hard for improvements to the NIWTP, participated in fish surveys, conducted water monitoring, counted birds, and all the other many conservation activities on behalf of the Santa Cruz River, the news of the topminnow’s return is exhilarating. It is also a clear sign of what highly treated effluent in the Santa Cruz and other effluent-dependent rivers can make possible. The success highlights what is at stake if the effluent goes elsewhere.

“Endangered species help shine a spotlight on how a natural system is functioning,” says Doug Duncan, fish biologist for the U.S. Fish and Wildlife Service. “To have this native species back is a big deal, because we never really gain natural populations. Their reappearance is an indication that we have a functioning ecosystem and are doing good things with our water. Now we need to keep water—clean water—in the river, and for that we need the public’s support.”

Sherry Sass agrees. “I think we can keep the river in the long term, but only if our larger community recognizes its value. We’re not there yet.”

The amount of effluent going into the river is at risk. Mexico has full rights to retain all of the wastewater that it currently sends to the US, which is more than two-thirds of the annual volume that is released into the river, and as of 2012 has constructed and expanded its own facilities to treat and keep its wastewater for domestic reuse in the state of Sonora.

“Long term, because of our climate, there’s just going to be more intense competition for our water, not less. In that context, the river’s rights are on the bottom of the priority chain,” Sass says. “There definitely needs to be some kind of recognition of the value of this riparian and aquatic environment that is so rare and disappearing in Arizona, or we will lose it. It will be gone.”

A Vision for the Future

“That’s where we come in,” says Stephanie Sklar, CEO of the Sonoran Institute, “We’ve spent over 25 years working on the Santa Cruz River on both sides of the border, so the river is part of our DNA. Needless to say, we’re in it for the long haul. However, if we are to ensure the future of the river, we need everybody in our region, from all sectors of our communities to join us. Whether you live in the San Rafael Valley, Ambos Nogales, or Marana, this is your river, but if we don’t fight for it, it could disappear. So, visit the river, feel a connection, and get involved. With an engaged community, up and down the river, with people who value it as a necessary resource for the future of our region—not just environmentally, but economically and culturally—we have the opportunity to turn the Santa Cruz River into the model for using effluent to restore an ecosystem and drive a regional economy. The return of the Gila topminnow speaks to this river’s ability to overcome adversity. Now that this tiny fish has returned, I think that anything is possible.”

Top image: courtesy AZGFD/George Andrejko
Bottom image: courtesy Jeff Smith

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