This is the Cheyenne River Reservation, home to the Lakota tribe of the same name, about half of whose members live here. It’s also home to Ziebach County, one of the poorest in the United States. I had come to Cheyenne River to meet the organizers of a small grassroots group called Mni, which means “water” in Lakota. They were in the middle of two weeks of ambitious water conservation work, constructing a series of small dams with help from two dozen or so volunteers from around the county. I had been told to look for a campsite, but I wasn’t sure where it was or what to expect.

I decided to head back to the highway to find cellphone service and began the bumpy ride that would take me there. It was then that I encountered an incongruous sight: a van parked by the side of the road, and a small film crew with a camera pointed at a petite woman in her sixties with long gray hair and cutoff jeans. I recognized her as Candace Ducheneaux, one of Mni’s leaders and an organizer of the water project. I pulled over and watched as she spoke to the camera.

The green of the hills was deceptive, she said. The appearance of lushness was only on the surface. People here had begun to notice the changing climate; after a drought that had persisted in the region on and off for 15 years, this summer’s heavy rains had inundated the South Dakota plains. But the dry ground, she said, was unable to absorb the large quantities of rain, which ran off into flooded creeks down the Missouri River, without ever replenishing the aquifer.

Mni’s goal, she explained to the camera, is to bring Cheyenne River’s water table back into balance. It’s an ambitious one: By constructing thousands of small dams in creeks and gulleys all over the reservation—essentially beaver dams built by humans—organizers hope to slow storm runoff long enough to enable the absorption of water back into the ground.

True to its Lakota roots, Mni is rooted in the tiospaye—the Lakota word for extended family—and comprises Candace, her daughters Karen Ducheneaux and Kyanne Dillabaugh, her son Luke, his wife Linda, and nearly all of their children. Standing on a hill with Candace, looking out over the hills that seemed to go on forever, I couldn’t imagine how they’d do it. But Mni is starting small, with a pilot project on a small parcel of family-owned land. If it’s successful, the Ducheneaux's plan is to build similar dams all over Cheyenne River and train workers from the other reservations in South Dakota, creating a model of water restoration that can be replicated anywhere.

“We have a million acres of tribal land here,” Candace says. “If we could convince the indigenous nations to begin water restoration—to unite in it—not only could we have a huge impact on the hydrologic cycle, but we could also set an example for the rest of the world.”