"HEMLOCK'S DOWN AND Trout Creek's coming up!"

My friend Sam Drevo, a Portland, Oregon–based kayaker, was on the phone. What he meant was "Let's go paddling." The Forest Service had recently jackhammered the 26-foot, 72-year-old Hemlock Dam out of Washington's Trout Creek, an indirect tributary of the Columbia River. Hemlock had drowned a Class V section of whitewater, and early spring storms were expected to raise the water level. With the dam gone, we had the rare opportunity to run new, potentially classic rapids. I flew to Portland.

Hemlock was the first of about 20 dams scheduled to come out of northwestern rivers over the next decade. The American era of river reclamation—which meant rampant dam building to increase the nation's power—lasted from 1900 until the mid-seventies, when the Army Corps of Engineers erected four dams on Washington's Lower Snake River. Those beasts went a long way toward wiping out what was once the most prolific salmon run on earth and sent enviros clamoring for a reversal. Finally, some 30 years later, the time seems to have arrived: 430 of America's 86,000 dams have fallen since 1999, and some big ones are on deck. Two behemoths are coming out of Washington's Elwha River next summer, along with four on Oregon's Klamath that are scheduled to fall by 2020. Last August, The New York Times proclaimed that the era of dam removal was upon us.

But that's a little simplistic, because there's more than one kind of dam. Most of the 430 removed thus far have been, like Hemlock, small structures that produced little electricity. The forthcoming removal of big dams on the Elwha and the Klamath is good for salmon lovers, but it's not necessarily a harbinger of snowballing dam destruction: It took 25 years of debate before the National Park Service committed to demolishing the Elwha dams. And some large hydroelectrics, like the four contested dams on the Lower Snake, provide so much power—enough to run Seattle for a year—that removal is, if not a pipe dream, a ways off. In March, the Obama administration, eager to wean the country off oil, pledged to develop clean hydropower by adding turbines to existing dams.

"People say dams are a thing of the past," says George Robison, dam-safety coordinator for Oregon's Water Resources Department. "That's delusional."

So what's the story? The era of dam removal or the era of clean hydro? Some think both are possible.

"The goal is to increase the total amount of power without building new dams," says Jeff Opperman, a hydropower expert with the Nature Conservancy. "We want to see a more holistic approach—increase hydro­power from existing dams, then look at removal for the little dams that might be giving only two megawatts."

In fact, according to American Rivers, there are tens of thousands of such dams—a number that has paddlers licking their chops. Hemlock certainly qualified as obsolete. Since its turbines were turned off in 1957, the dam had done little more than provide irrigation for farms and block steelhead. The day Trout Creek's natural flow was restored, someone spotted a steelhead upstream.

A few months later, in March 2010, I stood on the bank with Drevo and another kayak buddy. The stream was 20 feet wide, lined by Douglas firs, and dry—the storms had never materialized. For four miles we bloodied our knuckles scraping down the rocks: Come hell or low water, we'd paddle whatever new rapids existed. Finally, we arrived at the old dam site and found... a wide mudflat. We drifted through until the water threaded gently between some boulders. Trout Creek's newest rapid was a Class II. Next time, I'm bringing my fly rod.