AS I RETURN FROM the summit of Longs Peak, no one suspects I'm in costume. I can tell because no one is willing to come near me. Adventure racers in matching spandex unis pound on, heads bowed, when I shout, "Hey, just got back from the top. Wanna know how to do it right?"

What gives, man? Clearly I need a woollier, freaky-deaky scene. I need to go kayaking!

I get in touch with Landis Arnold, the 47-year-old owner of Wildwasser Sport, in east Boulder. He's more than happy to loan me a classic river runner. The fiberglass number we pull from the scrap heap behind his warehouse was handmade, circa 1977, by a local hobbyist who probably bought the mold at a hardware store. A little over 13 feet, double the length of modern playboats, the hull has a teeny bit of rocker, a pointy nose and stern, and fraying fiberglass below the waterline. She's the pinnacle of hydrodynamic design from the Age of Captain & Tennille.

This mission requires a new set of threads. Forget constricting drytops and a neoprene girdle. Try a striped wool sweater the color of Froot Loops and a rubberized spray deck with suspenders. A paddler buddy loans me a sparkly purple lid, and I load up my underpowered VW Golf, the kayak's tip and tail overhanging the bumpers, and hold up traffic all the way to Golden, Colorado, whitewater capital of the Front Range.

Out in the Golden whitewater park, a stretch of river right downtown, I discover that modern maneuvers (such as turns) are all but impossible, but the boat does cut into the current like an X-Acto knife through jelly. I delight in roaring downriver. Alone. Nobody actually runs rivers anymore. Instead, they cluster at the play wave—as spectators (today there's an amphitheater of parents watching their Junior Olympians train) or rodeo boaters (adults honing their "side-surf to space Godzilla to woo-woo").

I eddy out beside the jam-packed hole. The other boaters go bananas. "I had a kayak just like that!" many say, and they share old-timey stories about repairing their fragile boats over the campfire or teaching themselves to Eskimo-roll in the alligator-infested swamps of East Texas. Emboldened by their praise, I bump my way past other boaters and, to audible applause, pop vertical in a graceful "ender"—the kayaking equivalent of air guitar.

Next time, I really go for it—and really get it. I drop into the hole and my limousine is immediately stuck sideways. I try to swivel out backwards, but the nose of the boat, somewhere in Nebraska, sucks me back in. The same thing happens when I go forward. After a minute of pawing at a high brace, my shoulders quiver. Water seeps in through a crack widening beneath my legs. Bummer! I flip. Pop goes the spray deck, out comes me, away goes the boat. She fills with water and torpedoes downriver, bashing on boulders, causing a frightened elderly couple in an inflatable kayak to paddle like windmills for the shore.

Onlookers race down the bank to save my relic. I clamber ashore, sweater dripping like a wet dog. I have fiberglass rash on my wrists and possibly a busted toe, but I bound downstream anyway, dodging picnickers.

With the help of a ponytailed male sprinter, I finally retrieve the thing 300 yards downriver. The boat is kaput. Three cracks the length of my hand have opened in the bow, the furry underbelly, and halfway to the stern.

"You OK?" ponytail asks me.

"Yeah, yeah, fine, thanks," I blubber, water flushing out my nostrils.

"You know," he adds, "that's a nice boat."