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Bridge Creek, a narrow vein of water in the eastern Oregon desert, is a hard place for a fish to love. On the bare, steep edges along this stretch of creek lie scraps of plastic irrigation pipe, fragments of a wooden chair, and sun-beaten cans of the local down-market brew. The creek itself, confined to the edge of its floodplain more than a century ago by energetic homesteaders, cuts deeply into the soft soil, with few of the cool, shady pools and riffles native steelhead trout need.

Restoring this creek—and countless other hard-used streams in the arid West—to something resembling good trout habitat is a costly, complex challenge, requiring either bulldozers or decades of patience. But biologist Chris Jordan of the Northwest Fisheries Science Center in Seattle is studying a willing, able, and cheap labor force: beavers.

Fur trappers decimated the West’s beaver populations in the 1800s, but after fur hats went out of fashion, the species began its long comeback. Today, in much of the country, beavers are so plentiful they’re considered pests. Oregon, however, despite its nickname—the Beaver State—is an exception, and they remain relatively rare in the region.

On Bridge Creek, Jordan has invited the toothy rodents back. He and his crew have pounded rows of wooden posts into the stream, allowing more beaver dams to gain a toehold in the fast-moving water. Within a year stretches of the creek had more beaver activity, more pools, and more of the sediment needed for riparian vegetation. “Fish and beavers have lived together for hundreds of thousands of years,” says Jordan. “Beavers make stream habitat that fish are quite happy with.”

As research by Jordan and others reveals beavers’ benefits for streams, some conservationists and land managers are encouraging the rodents to get to work, both to restore fish habitat and—as climate change triggers more frequent and deeper droughts in the West—slow the flow of precious spring snowmelt. “Beavers create a lot more habitat than they chew up,” says Steve Zack, a conservation scientist with the Wildlife Conservation Society.

Zack, who studied a successful state-run reintroduction program in Wyoming, says beaver-driven restoration has huge potential. “We’re just starting to understand the profound impacts beavers had and can have,” he says. “They’re the ultimate ecosystem engineers.”