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“What more measurable proof does any decisionmaker need as a call to action to do more than posturing to help the San Pedro?� asked Robin Silver, co-founder of the Tucson-based Center for Biological Diversity. “It’s time to fish or cut the bait if the San Pedro River, the last free flowing undammed river in the desert Southwest, its millions of dependent neotropical songbirds and many dependent endangered species, are to be saved.�

The Summers well, lying on the river about seven miles downstream of Fort Huachuca, reported “D� for dry as of June 30, U.S. Geological Survey records show. The USGS maintains and monitors the network of wells — monitoring required by a 2023 court order.

Maricopa County Superior Court Judge Mark Brain required the monitoring of nine wells and four stream gauges as part of an order establishing minimum flows on the river. The river running north from the Mexican border nearly to Benson comprises the San Pedro Riparian National Conservation Area. Brain’s order was quantifying the amount of water the river is legally entitled to.

“As the monitoring wells are making clear, development around the Sierra Vista area and associated with Fort Huachuca is killing the San Pedro River — monitoring wells continue to show declines and now we have one that has dried up entirely,� said Sandy Bahr, director of the Sierra Club’s Grand Canyon Chapter.

“We should not wait until the river is bone dry like that monitoring well before we do something about it,� Bahr said. “We must limit groundwater pumping in the region. The San Pedro River is critical for people and wildlife alike. We cannot afford to lose this river to development.�

The ÃÛÁÄÖ±²¥ Department of Water Resources, which is facing two lawsuits from the Center for Biological Diversity over its management of the San Pedro, declined to comment on the dry monitoring well.

“We will not be commenting on any matter related to pending litigation,� said ADWR spokesman Doug MacEachern.

Jamie Macy, associate director of USGS’ ÃÛÁÄÖ±²¥ Water Science Center, didn’t return a phone call or an email from the Star seeking comment on the dry well. Officials of the U.S. Bureau of Land Management, which owns and runs the San Pedro conservation area, also didn’t respond to an emailed request for comment.

Angela Camara, a spokeswoman for Fort Huachuca, also hasn’t responded to an email from the Star seeking comment on the dry well.

Brain set the minimum flow levels to ensure the San Pedro, its riparian landscape and a tributary are protected. His rulings in August 2023 and December 2024 were also aimed at safeguarding federally reserved water rights on the river.

Brain’s rulings formally quantified those rights by setting minimum levels in monitoring wells and stream gauge flows. His rulings aren’t final, in part because they’re part of a much broader court case covering formal adjudication of water rights for the entire Gila River Basin that includes the San Pedro. But ADWR has cited Brain’s findings in a groundwater model report for the Upper San Pedro River Basin that it prepared in 2023.

Before the dry monitoring well was discovered, levels in five of the nine monitoring wells and annual flows as measured by three stream gauges on, underneath and near the San Pedro and a tributary had already fallen below minimums set by Brain.

Some environmentalists, including Silver, have pushed for downsizing of Fort Huachuca, whose pumping of groundwater has increased in recent years. Officials have also focused on well pumping by a large copper mine in Cananea, Sonora, as a potential source of the river’s problems in ÃÛÁÄÖ±²¥.

The San Pedro Riparian National Conservation area covers about 57,000 acres, and runs north for about 40 miles from the Mexican border to St. David, just south of Benson.

The river in that area is known as one of the world’s premier hot spots for migratory birds and as an excellent haven for large and small mammals. It plays host to numerous federally protected species, including the endangered Southwestern willow flycatcher, the threatened Western yellow-billed cuckoo, the threatened northern Mexican garter snake and the endangered Huachuca water umbel.

The river’s future has long been considered imperiled because of continued groundwater pumping to serve ÃÛÁÄÖ±²¥ and businesses in the Sierra Vista area, and to a much lesser extent by the region’s farms, which have long been declining in number and scope.

The San Pedro has long run a chronic deficit between demand by people for the groundwater underlying it and the groundwater supply. The deficit between pumping and recharge has declined from about 33,000 acre-feet in 1990 to about 20,000 acre-feet in 2023, due mainly to decreased agricultural pumping, a December 2024 report from the ÃÛÁÄÖ±²¥ Department of Water Resources shows. But many scientists have long said the river could still dry up in the future unless the deficit is drastically reduced or eliminated.