The San Pedro River's cottonwood-shaded corridor provides critical stopover habitat for millions of migrating birds each year. It is one of only two major rivers that flow north out of Mexico into the United States and is one of the last large undammed rivers in the Southwest.

The San Pedro River basin is home to 84 species of mammals, 14 species of fish, and 41 species of reptiles and amphibians. Species such as the jaguar and black bear stalk the region’s forested mountains while the Mexican gray wolf and black-tailed prairie dog reside in the expansive grasslands.

Why the Conservancy is Working Here
The mild climate around the San Pedro has attracted tens of thousands of newcomers and sprawling development in recent decades along certain parts of the river. Increasing human demands for water, for both domestic use and irrigation, is lowering the water table. Now, parts of the San Pedro are no longer perennially flowing.

Consequently, native streamside plants like cottonwoods are crowded out as adaptable invasive species (such as tamarisk) with deeper root systems thrive. Animal species, particularly birds, suffer as water is drawn deeper underground.

What the Conservancy Is Doing

• The Conservancy is working with Mexican partners and Upper San Pedro Partnership to address water conservation for the upper portion of the San Pedro Basin.
   
• The San Pedro River wet/dry mapping is a community effort to track the river’s health by monitoring the persistence of surface water during the driest time of each year. It is created by recording the end points of every wet section of the San Pedro River during June each year. Results will allow community water managers to monitor flow patterns and adapt strategies to restore year-round flows, preventing further deterioration of the ecosystem.
   
• Some streams in the Lower San Pedro River watershed are so healthy they are the site of a massive fish reintroduction effort. At Muleshoe Ranch Cooperative Management Area where the Conservancy rehabilitated a former cattle ranch, healthy populations of native loach minnow, desert pupfish and spikedace are thriving.
   
• At the Conservancy’s Three Links Farm near the Upper San Pedro, a 90 percent reduction in agricultural water use over the last five years is helping the river: cottonwood seedlings dot the riverbed and shores, indicating that natural flows are intact and the river is doing well. 

San Pedro River Facts

• Location: The San Pedro flows north from the Mexican state of Sonora to join the Gila River in Arizona.
• Plants: Fremont cottonwood, Goodding willow, velvet mesquite, sacaton, and the Federally endangered Huachuca water umbel
• Animals: 84 species of mammals, including jaguar, coatimundi, bats, beaver, mountain lion, and many rodents; more than 41 species of reptiles and amphibians, including Sonoran tiger salamander and Western Barking Frog; more than 100 species of breeding birds, including the imperiled yellow-billed cuckoo; and, seasonally, more than 250 species of migratory birds. Remaining native fish species include the Gila chub which is proposed for federal listing as endangered, and the longfin dace, desert sucker, roundtail chub, Sonora sucker, and speckled dace.

Nature picture credits (top to bottom, left to right): San Pedro River © Sally Clement; Huachuca water umbel © William R. Radke/USFWS; Map & Watershed Graphic © The Nature Conservancy.