WHEN I FIRST MET RUSKEY, a few days before our trip, I was worried about how he'd react to my little scheme. After all, it would be his show, and he'd be the one who'd have to answer for my lunacy.

Ruskey's a riparian philosophe, a Renaissance man of the Delta. In addition to being a great paddler, he's a musician, an artist, a poet, a gourmet chef, a master woodworker, and, almost incidentally, a businessman, sole proprietor of the Quapaw Canoe Company. I visited him at his offices near the banks of the Sunflower River in the blues capital of Clarksdale, Mississippi. Ruskey runs Quapaw out of the ground floor of an old industrial warehouse—the Cave, he calls it—which he has wallpapered with Army Corps maps and cluttered with snake skins, turtle shells, sturgeon skeletons, and other bric-a-brac from his river forays.

With Clarksdale's ridiculously good local station, WROX, blasting on his truck radio, Ruskey and his wife, Sarah, took me around town—to the famous crossroads where they say Robert Johnson made his deal with the devil so he could play guitar, and to Ground Zero, a popular juke joint Morgan Freeman helped start up a few years ago. Then we breezed past the old Stovall Plantation, and I watched a low-flying plane dust the same fields where Muddy Waters grew up as a sharecropper. We drove on top of the levee and wound down to a secluded spot on the river. There we sat at dusk, dangling our feet in the water, eating stinky French cheese and gazing out toward Montezuma Island.

"From here," Ruskey said, "there isn't a bridge for a hundred miles. It's all uninterrupted wilderness and floodplain. On most of these islands, you've got nothing but deer, bear, and boar roaming in enormous hardwood stands. And the beautiful part is ... no one knows about it!"

In his own understated but tenacious way, John Ruskey has devoted most of his adult life to understanding the science, engineering, history, politics, and literature of the lower Mississippi (that is, everything below Cairo, Illinois, where the Ohio empties into the river). As Ruskey likes to say, he's got mud in his blood. He's extremely laid-back in his mannerisms—a blues aficionado, he used to be the curator of Clarksdale's Delta Blues Museum. But on the subject of the Mississippi he can wax rhapsodic to the point of religiosity.

River Jesus, I came to call him. He noted how Einstein's son spent his whole life studying the chaos and complexity of rivers. He's been known to lasso giant floating trees and ride them downriver, like Slim Pickens straddling that atom bomb in Dr. Strangelove. With a straight face, Ruskey told me, "Rivers connect us all."

In the summer of 1982, when Ruskey was 18, he and a friend decided to go to the headwaters of the Mississippi and build a wooden raft. For five months, they floated the river; they were aiming for the Gulf of Mexico. But one February night, close to the Tennessee–Mississippi line, their raft smashed to pieces on a concrete TVA pylon. Clinging to the wreckage, Ruskey and his friend drifted for miles in the frigid current. Hours later, they washed up on a deserted island and built a bonfire to signal for help. The Coast Guard eventually picked them up.

"That whole experience," Ruskey told me, somewhat sheepishly, "drove the river deep into my soul."

Certainly it made him more respectful of the Mississippi's capacity for treachery. I've seen it in his face every moment of our canoe trip, a steady hypervigilance in back of his seeming serenity. River Jesus is calm, but never cavalier.

"In the Mississippi," he said, "when things go bad, they go bad in a hurry. This is the Himalayas, the big mountain of rivers. When you 'fall' off this peak, you don't just fall a few feet. You're going to end up miles downstream. And unless you really know what you're doing, you're probably going to end up a floater."

After he said that, I felt doubly stupid about wanting to swim the Mississippi. But when I finally worked up the nerve to broach the subject with Ruskey, his reaction surprised me.

"Awwwwrahhhht!" he said, fairly brimming with enthusiasm. "You're a man after my own heart. A baptism! Everybody should swim across the Mississippi, at least once. It's a God-given right that ought to be written in the Constitution."

"You think so?"

"Well, you gotta go about it in the right way. Pick the right time and place. You have to know where the wing dikes are, where the eddies and shoals are. And you have to watch like a hawk for barge traffic. But it's an excellent thing to do."

"It ... is?"

"Look, I get in there all the time. The Mississippi's the mirror of our soul, a barometer of our national health. If we can't swim in it, then we're really in trouble."

Which brought up a terrifically pertinent question. "How dirty is it in there?" I asked. "Am I going to end up with a huge, honkin' dioxin goiter on my neck?"

"No," Ruskey replied. "Tests in this stretch of the Mississippi show up negative for every major contaminant. And toxicology studies have shown it's safe to eat fish in the lower Mississippi—which you can't say for most of America's rivers and lakes. You don't want to swim directly downstream of places like the Memphis wastewater plant, or else you're going to get a mouthful of coliform bacteria. But most places on the lower Mississippi, the water's surprisingly clean."

Yet, as Ruskey could tell, I remained skeptical. "Hey, I'm not saying you'd want to drink it," he said. "But it's perfectly safe to swim."

Then he looked at me with mischief in his eye and said, "I got the perfect spot in mind for you."