The Gila River: The Southwest’s Threatened Eden

Stretching over 600 miles across two states, the Gila River is an iconic natural feature of the American Southwest. From its origin in the pine forests of the Black Range of western New Mexico to its confluence with the Colorado River in southwestern Arizona, the river is fed by six major tributaries. Winding through iconic ecosystems including the arid Sonoran Desert, its waters support forests of willows and massive cottonwoods, vital habitat for more than 300 species of migratory and breeding birds, including many found nowhere else in the United States, such as the common black-hawk and northern beardless-tyrannulet. And high-elevation portions of the watershed host the last remaining strongholds of many native fish, such as the endangered Gila trout.

Map of the Gila River watershed
Map of the Gila River watershed
Kmusser, CC

However, what was once the lifeblood of the Sonoran Desert has been drained and diverted to support the ever-growing metropolises of Phoenix and Tucson. West of Phoenix, the river is usually a dry bed and where water still flows, the fragile ecosystem is assaulted by invasive species, drought, grazing and mining, which are only exacerbated by the growing effects of climate change. As a result, 21 of Arizona’s original 36 native fish species are either extinct or federally listed as threatened or endangered.

Degradation of a River System

Confluence of Bonita Creek and Gila River in Gila Box Riparian National Conservation Area, in Graham County, Arizona; seen from the vicinity of the Kearny campsite monument. The Gila flows toward the camera, center and left of center; Bonita Creek flows left to right, through the canyon whose far wall is visible behind trees at the right edge of the photo.
Confluence of Bonita Creek and Gila River in Gila Box Riparian National Conservation Area, in Graham County, Arizona; seen from the vicinity of the Kearny campsite monument. The Gila flows toward the camera, center and left of center; Bonita Creek flows left to right, through the canyon whose far wall is visible behind trees at the right edge of the photo.
Ammodramus

Hydrology of the Gila

Gila topminnow Poeciliopsis occidentalis
Gila topminnow Poeciliopsis occidentalis
Gila topminnow (© Brian Gratwicke)

Because snowpack and water-bearing storms have historically varied so much from year to year, the Gila ecosystem evolved to cope with incredible variation in flow intensity and duration. However, under the current human-dominated system, the river is essentially in permanent drought from dams and groundwater pumping, and the effects of climate change increasingly exert their own pressure.

Middle fork of the Gila River NM
Middle fork of the Gila River NM
Joe Burgess

Spring flows annually reshape river bottoms. In early spring, sedimentation increases, but by late spring, rapidly receding flows carry away fine sediment to reveal cobble bars — a micro-ecosystem with nooks and crevices sheltering invertebrate prey and smooth surfaces perfect for egg-laying, providing fish like the endangered spikedace reproductive habitat. Specific cues of temperature and flow intensity trigger these species to spawn. Once larvae hatch, the spring flow has already started to lessen, so the larvae avoid the brunt of the strongest currents. Every step of native fish reproduction happens in delicate coordination with the snowmelt-fed spring flow, but by the end of the century, the American West may be functionally devoid of snowpack due to climate change.

These varied flow patterns also maintain the structural integrity of the native cottonwood-willow forests that line the Gila system’s rivers and streams, essential breeding habitat for the endangered southwestern willow flycatcher and threatened western yellow-billed cuckoo. High-level flows breach the riverbank, soaking water into the ground outside the immediate vicinity of the shore, and thereby replenishing groundwater. In the arid Sonoran Desert, such flooding events are essential for survival and recruitment of riverine trees, understory vegetation, marshes and cienegas. In flood season, rushing water can remove patches of undergrowth, creating structurally diverse mosaics of open areas and dense vegetation. These river-based engineering processes establish habitat for hundreds of resident and migratory birds and for wetland-partial fishes like the endangered Gila topminnow.

When the health of this vegetation is compromised, associated wildlife suffers. Where the loss of spring floods threatens the growth potential of native cottonwood and willow seedlings, exotic tamarisk quickly outcompete them.

Introduced Threats

Perhaps most importantly, loss of flooding has facilitated the spread of introduced eastern fish, bullfrogs and crayfish and these species have decimated native fish communities. Predatory fish like largemouth bass and green sunfish have eaten some native populations out of existence, while crayfish and bullfrogs threaten the ESA-listed Chiricahua leopard frog and northern Mexican garter snake. Some exotics like catfish and mosquitofish displace natives by outcompeting them for resources, while others hybridize with them. In this manner, nonnative rainbow and brown trout pollute the gene pool of endangered Gila and Apache trout, Arizona’s only native salmonids.

These exotics would likely have fared poorly under the seasonal floods and periodic powerful currents that historically characterized he Gila. But the present tamed and diminished river presents perfect conditions for them to flourish.

Conserving the Gila

Gila River from the air in Komatke Arizona
Gila River from the air in Komatke Arizona
Dicklyon, CC

Conservation groups like Defenders play an important role as advocates and watchdogs. Alongside our partners, Defenders monitors federal actions and development proposals to make sure they are as “riparian-friendly” as possible. In our recent submission of federal comments to the U.S. Forest Service, we disparaged their forest plan for allowing more cattle grazing instead of less in sensitive riparian areas.

A huge win came in June when the New Mexico Interstate Stream Commission voted against permitting the construction of a major new dam on the New Mexican portion of the Gila River. This victory was the result of decades of campaigning by conservationists, elected officials, tribes, landowners and recreationalists who fought to keep the upper Gila wild and scenic.

State and federal agencies are working to protect the Gila’s precious biodiversity. The Arizona Game and Fish Department works to eradicate exotics from select areas, breed endangered native fish like desert pupfish in hatcheries and refuge ponds, and reestablish lost populations. The U.S. Forest Service has taken steps to reduce the grazing footprint on public forest land by implementing pasture rotation and limited seasonal use, reducing herd density and fencing vulnerable or degraded riparian areas.

The Verde River Exchange has protected the water table in this vulnerable Gila tributary by establishing a water-offset program. Under the exchange, landowners can purchase water credits to offset their usage. These “water offset credits” are created when certified landowners voluntarily reduce their own usage. Several businesses in the Verde Valley have become important actors in reducing their water footprint through the exchange.

Humpback chub
Humpback chub
USFWS

Partnerships also play an important role in conservation of water and biodiversity. The Cochise Conservation & Recharge Network takes an engineering approach to replenishing groundwater storage in the San Pedro River watershed by constructing a series of water recharge facilities along 25 miles of the San Pedro River. Collected stormwater is treated and the effluent re-injected underground to replenish the groundwater supply. In this way, water extracted from the San Pedro for human use in Cochise County can eventually make its way back into the river.

The City of Tucson’s Santa Cruz River Heritage Project releases purified wastewater into the Santa Cruz River, where it supports a newly established population of endangered Gila topminnow. Like the Cochise Network, this is an excellent example of large-scale water recycling.

Hope for the Future

Gila trout boodfish
Gila trout boodfish
© Robert H. Pos/USFWS

Fortunately, advocates have the remarkable resiliency of the river on our side, which evolved in a land of harsh droughts and raging floods. Despite a century of abuse, populations of most native species survive, waiting for better times. We hope that by advocating for the Gila, its tributaries and other southwestern rivers, more and more people will recognize the unique value they hold. With enough dedication and collective action, we can give the rivers — and the exceptional biodiversity they support — what they need to survive.

Reed Wester-Ebbinghaus is a student at Carleton College who interned this summer with Defenders’ Southwest program.

Wild Without End

Defenders is committed to the sustainable conservation of…

Defenders of Wildlife

Written by

Defenders works on the ground, in the courts and on Capitol Hill to protect and restore imperiled wildlife across North America.

Wild Without End

Defenders is committed to the sustainable conservation of wildlife for future generations.

Defenders of Wildlife

Written by

Defenders works on the ground, in the courts and on Capitol Hill to protect and restore imperiled wildlife across North America.

Wild Without End

Defenders is committed to the sustainable conservation of wildlife for future generations.

Medium is an open platform where 170 million readers come to find insightful and dynamic thinking. Here, expert and undiscovered voices alike dive into the heart of any topic and bring new ideas to the surface. Learn more

Follow the writers, publications, and topics that matter to you, and you’ll see them on your homepage and in your inbox. Explore

If you have a story to tell, knowledge to share, or a perspective to offer — welcome home. It’s easy and free to post your thinking on any topic. Write on Medium

Get the Medium app

A button that says 'Download on the App Store', and if clicked it will lead you to the iOS App store
A button that says 'Get it on, Google Play', and if clicked it will lead you to the Google Play store