Early one May morning, after a night of partying in a friend's Council Crest home, Jay Rubin, 21, finally got lucky. He persuaded four friends to bushwhack their way through blackberries down the hill past the YMCA and--after stripping down to their skivvies--into the Willamette River, spooking a crew of dragon-boat paddlers training for the Rose Festival races.

Equipped with only a dry bag for their clothes, the quintet swam the Willamette and continued east, reaching the summit of Mount Tabor, their makeshift finish line, a couple hours later.

Afterward, Rubin posted cryptic, unsigned fliers around town urging others to follow in his soggy footsteps and make the cross-town trek. There were--and still are--only three rules: no motors or "equipment," no money, no bridges. Adventurers are forced to rely on muscle and brain-power, and their biggest obstacle is the river. Rubin, a onetime Boston University American Studies major, suggested they "Huck Finn it" using a makeshift raft.

Now just a few months old, Rubin's urban ritual (he has no idea whether anyone was inspired to make the journey) has gone legit. With the permission of the Coast Guard and the blessing of the City of Portland, this double-dog dare has a name, the Portland Challenge, and a date, Aug. 24. Naturally, it also has a charity beneficiary--a planned orphanage in Tanzania. It even has a celebrity participant: Columbia River swimmer Christopher Swain has signed on to take the plunge--sans wetsuit.

The course has changed to appease city safety standards--it will now run from the Laurelhurst Park annex to Waterfront Park and will include life jackets, but the spirit is the same, Rubin says.

"This is maybe one of the first things I've done that's constructive and sort of ridiculous," he laughs. "There's no good reason to swim the Willamette."

Indeed, there may be good reasons not to swim the Willamette--namely, toxic pollutants like mercury, dioxin and lead. "I wouldn't swim it," says OSPIRG's Laura Etherton, whose group is campaigning to clean up the river. But Dennis Ades, Willamette Basin Coordinator for the state's Department of Environmental Quality, says such toxins, which are found in the river's fish and sediment, pose little risk to swimmers. As for the bacteria found in any body of water, Ades says the Willamette fares well when compared with other local rivers: "It's actually in better shape than a lot of its tributaries."

Absent a sewage spill, Ades says on a dry August day the biggest threat to swimmers may be jet-skis, not pollutants.

Whatever the risks, Rubin hopes Portlanders will see jumping into the river as a literal leap of faith. "Make that jump for Portland," Rubin enthuses, "and Portland will love you back."