San Pedro River southeast of Phoenix © Harold E. Malde

Places We Protect

San Pedro River


Cross-border collaborations bring lasting results to one of America’s last large undammed rivers.

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 protected four private properties totalling 613 acres that were some of the largest unprotected tracts along the river. Now these private lands make up part of a protected 10-mile-long wildlife corridor linking the Galiuro Mountains to the Rincon and Catalina Mountains. 
  • An innovative project involving Cochise County, the U.S. Army’s Fort Huachuca and the Conservancy is showing great potential to capture stormwater runoff and replenish the aquifer that supports river flows. The Cochise Conservation and Recharge Network has developed one recharge facility and plans to develop such facilities at three other sites along the river on properties the Conservancy purchased for the effort.
  • The Conservancy acquired two key tracts of private land for supporting the health of the river and sustaining the upper San Pedro aquifer: the 1,811-acre River Stone Ranch and 285-acre Mansker tract. Since work began on the San Pedro, more than one-third of the river corridor is now protected and water savings in the lower basin exceeds 14,000 acre-feet annually.
  • Volunteers are helping map the flows of the San Pedro. The results of the mapping, conducted during June of each year, allow 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.