"Either of you want $20 to shuttle us down to Massacre Rocks?" I'm pointing the question in the direction of two dudes fishing off an aluminum dock beside the boat ramp. They twist around in their camp chairs and eye me suspiciously, taking in the red canoe strapped to the roof of our car. The skinny one, after a beat, says, "No bro, we're fishing hardcore." We try again at a different dock, where our mark replies that he just got off work and shouldn't even be awake. Implying, I guess, that he's got enough work, and a man has a right to kill a few hours with a fishing pole and a beer at 9 a.m. after an all-night shift at the potato plant without worrying about a couple of out-of-towners and their fancy canoeing plans.

Finally we persuade the manager of the Falls Motel to run our shuttle. As we drive, she explains that most folks in American Falls work at the Simplot potato plant in Aberdeen, or the Lamb Weston plant right in town. On the right side of the interstate stretch fields shaped by the immense sweeping arms of center-pivot irrigation. On the left lies the abrupt river canyon, the Snake itself visible on the occasional bend.

Idahoans call the Snake the "Working River," in contrast to its northern sibling, the Salmon, which tumbles through largely idle wilderness to the north. The Snake gets no such free passage. Impounded and diverted throughout its course, it is the root of commerce in the southern Idaho desert. Launching less than 100 yards from the massive American Falls Dam hydropower complex for a purely recreational trip—the fifth leg of Red Canoe's Snake River odyssey—feels a bit frivolous. Even the fishermen on shore are making the river give something up.

I'm here with my brother Will, and we're both a little groggy—his sleep deprivation from caring for a newborn, mine from carousing with a bridesmaid at our sister's wedding. We haven't canoed together for a decade, but our partnership is hard-wired from childhood. We slip into an easy rhythm, pushing steadily downstream, aiming for the takeout by lunch. We'll drive around Lake Wolcott to paddle the next free-flowing stretch to Burley by nightfall. Red skips reservoirs.

On one bend the left canyon wall recedes, opening onto a farm where a line of concrete slabs sunken into the bank holds back erosion. About halfway along, someone has pushed a few old cars onto the bank to do the same, and they lie half-covered, stripped by the current to smooth rusted steel. One of the hulks has drifted into the channel, serving as an island perch for a flock of white pelicans. As we paddle up, they string away and we see it's an old blue Wagoneer, seats gone but the steering wheel still arcing above the water.

We'd heard there are a few rapids in here, but we'd also been told that you could float this stretch in an inner tube. So when the roaring we had thought came from the interstate reveals itself as a river-wide shoal, we hem and haw, but decide not to scout. As the current takes hold of Red's battered hull and slings us forward, the rapid suddenly looks serious. All 100 yards of the riverbed tilt downstream; the water sluices headlong over shallow, basalt reefs, and it's far too late to get ashore. Wide-eyed, we backferry our way down a Class III rapid only the most sadistic tuber would attempt, and at the bottom we celebrate as if we'd run a stout Class V.

It's an impetuous thrill that feels like the antidote to the agri-industrial complex around us, and we're glad someone is out here meeting the Snake on its own terms. We're resigned to being the only ones until that afternoon on our second leg, we spot a bit of commotion; people splashing around at the base of a short, broken falls. Paddling over to investigate, we find a group of kids busily bumping their way down the rapid in inner tubes. Then there's the van that rolls up, the side door wide open, a guy sitting there with a mask and snorkel on, dangling his swim fins over the dirt road.