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Among southwestern rivers, the San Pedro is an anomaly in that it lacks dams. Thanks to its ability to flow unfettered, and to extensive federal and private conservation efforts, the river is one of the crown jewels that lures birders to southeastern Arizona in pursuit of such exotic quarry as gray hawks, Cassin’s sparrows, and northern beardless-tyrannulets.

In 1988 Congress designated about 40 miles of the San Pedro a National Conservation Area managed by the Bureau of Land Management, complete with federally protected water rights. Accordingly, the BLM curtailed cattle grazing in the river corridor. Riparian plants thrived. Birds noticed: A 2003 study documented increases in dozens of breeding species along the river’s cottonwood-lined banks. 

“The San Pedro is the undammed major river corridor within the intermountain West,” says Tice Supplee, director of bird conservation for Լ����Ƶ Arizona. “Because it still has so much intact riparian community, it is a tremendous stopover for neotropical migrants.”

But the Arizona Department of Water Resources (DWR) is considering granting an authorization that would allow the construction of thousands of new homes in the area. Developers in nearby Sierra Vista have proposed building a subdivision that would support almost 7,000 homes within 20 years. The homes would be supplied with water by pumping more than 3,000 acre-feet of groundwater per year (an acre-foot is the volume of one acre of water one foot deep).

Wells in the upper San Pedro Valley already suck up an estimated 6,000 acre-feet per year more than is naturally recharged from rainfall and snowmelt. To avert further losses, Լ����Ƶ Arizona, the Grand Canyon Chapter of the Sierra Club, and the BLM have lodged formal objections to the proposed project with the DWR, which has the authority to rule that there is inadequate water to supply the proposed houses for the next century. The BLM is concerned about surface water because it manages the river, but the state agency may well take only underlying groundwater into account, since state law doesn’t recognize any legal connection between a river and the watershed that recharges it. So the DWR might rule that the developers can pump groundwater at will without considering the existing water rights that govern the river’s flow.

“You’re looking at [an annual] 3,000-acre-foot deficit in a groundwater basin that’s already accruing substantial deficits,” says BLM hydrologist Bill Wells. “We’re just trying to say we believe there is a connection between the river and the groundwater.”

Groundwater depletion is a big problem in the arid West, nowhere more so than in southern Arizona, where hydrologists have documented how excessive pumping can dry up springs, streams, even entire rivers. West of the San Pedro, the Santa Cruz River was once an equally lush swath until Tucson’s thirst for groundwater converted much of it into a barren stretch of sand.

 On the San Pedro, the project could jeopardize years of drop-by-drop efforts, including nearby Army Fort Huachuca’s strict landscaping limits, water recycling, and low-flow plumbing fixtures. Says Tricia Gerrodette, president of the Huachuca Լ����Ƶ Society, “Whatever conservation gains are achieved would be more than wiped out.”