Horseshoe Reservoir: An Opportunity to Restore 

Audubon StoryMap explores riverside habitat rehabilitation options within footprint of reservoir on the Verde River 
Phainopepla. Photo: Peter Thiemann/Audubon Photography Awards

An hour and half drive northeast of Phoenix, you’ll find yourself among the mesquite bosques and Sonoran desert of the Tonto National Forest, a region home to the Verde River and one of Arizona’s Important Bird Areas (IBA), the Salt and Verde Ecosystem. Here, you can find enchanting birds like Phainopepla, Vermilion Flycatchers, and Lucy's Warblers.   

It’s also home to the Horseshoe Reservoir, formed in 1944 when Horseshoe Dam was built by the United States Government and Phelps Dodge corporation to provide a water supply to help meet the water needs of industries (like mining), agriculture, and the Phoenix area's growing population. When it was built, along with its sister dam, Bartlett (built in 1939), the Verde River behind the dams turned into reservoirs, flooding the native riverside trees and shrubs, submerging archaeological and Indigenous sites, and transforming the landscape. As you will see in the StoryMap, Horseshoe Reservoir is upstream of Bartlett Lake.   

Reservoirs like Horseshoe and Bartlett capture rain and snowmelt, acting as a holding tank and controlling how much water is allowed to flow downstream. Of course, this impacts a river’s ability to flow naturally and greatly alters habitat. But dams and reservoirs also allow water to be stored and then released later so that communities, farmers, businesses, and others have access to water when they need it. A Habitat Conservation Plan (HCP) has been implemented by the Salt River Project (the entity that manages the water operations at the two dams) with guidance and approval from the United States Fish and Wildlife Service to protect and preserve habitats for threatened and endangered species—like the Southwestern Willow Flycatcher, Yellow-billed Cuckoo, and Bald Eagle—affected by Bartlett and Horseshoe reservoirs.     

The Horseshoe Reservoir not only stores water behind its dam, but has also collected sediment—soil and debris that flows from the landscape and into the Verde River. Years of sediment build-up at the reservoir has shrunk the water storage capacity of Horseshoe Reservoir. To address this problem, the United States Bureau of Reclamation worked with the Salt River Project and stakeholders to conduct an analysis to figure out how to best deal with the sediment issue, as well as to explore how to protect water supplies and adapt to climate change. One of the most attractive options from the study was to raise the height of Bartlett Dam to replace the lost water storage capacity from sediment accumulation in the Horseshoe Reservoir.  

Then what should become of Horseshoe Reservoir? That’s where our StoryMap comes in.    

The StoryMap explores what might be possible if Horseshoe Dam is allowed to pass the water from the Verde River through it—and down to Bartlett Lake—and revert to acting more like a river, instead of a reservoir. We wanted to know: what riverside, marsh, wetland, or desert habitat could be established in the footprint of Horseshoe Reservoir if there was a dynamic and ever-changing river, instead of a lake? To better understand the possibilities, we conducted research and wrote a report. It includes case studies of native vegetation projects at reservoirs from around the country. 

To visually explain the report, we produced a StoryMap. You will see that it is broken up into eight different sections, taking you on a tour through the Verde River watershed and potential sites for native vegetation to grow within the Horseshoe Reservoir footprint; there are also digital renderings of the potential vegetation sites.   

This past winter, rain and snow filled Horseshoe Reservoir, according to water gauges (see Snoflo’s daily monitoring report). The greatest challenge for any revegetation is the fluctuations in water levels at the reservoir. Current reservoir operations draw down the water level to near empty in most summers as part of the Habitat Conservation Plan to prevent non-native fish from spawning in the reservoir. Water from heavy snowmelt like this past winter fill it up for many months well into the summer. The result is dramatic swings in surface water elevation between dry and wet years, creating tough conditions for plants to grow and survive. Climate change impacts on the Verde River watershed are expected to only exacerbate the swing from dry to wet periods.  

So how do we deal with uncertainty? I invite you to explore the StoryMap I created with proposed solutions from the Horseshoe Reservoir Habitat Restoration Study by National Audubon Society Southwest Director of Bird Conservation Tice Supplee and Restoration Ecologist Mark Briggs, with support from The Nature Conservancy and the Salt River Project.   

The StoryMap is an engaging way to learn about these complex environmental issues. And as decisions about water management are made, we will need as many voices as possible, including YOURS, to play a role in shaping our water future in the West, for people and birds.