Yellowstone's kayaking policy dates back to 1950, when a ban on boating was adopted as a way to cut down on overfishing. Since then, the only legal runs of Yellowstone's rivers have been search-and-rescue missions. A single week in 2009 saw two such efforts: One after a park employee accidentally drove her car off the Tower Junction bridge, and another for a Boy Scout who was knocked into the Black Canyon while playing near the river. Troy Nedved, a Park Service employee and class V kayaker, led both rescue efforts, eventually recovering a skull from the car wreck and a white tennis shoe belonging to the Boy Scout. Drowning is the leading non-vehicular cause of death in national parks.

Even so, only two parks in the country have what Colburn calls "blanket bans" on whitewater kayaking: Yellowstone and Grand Teton, though the bans aren't comprehensive. There's a a calm three-mile channel of the Lewis River in Yellowstone that's legal to paddle, and a much longer section of the Snake River in Grand Teton. Individual parks set their own policies regarding recreational activities, and in most, kayaking, canoeing and rafting are grandfathered in. Often paddling is "supported and celebrated" by park managers, Colburn says.

But though recreation is integral to many parks' identities, Yellowstone officials say they have to balance it with their primary goal of protecting and conserving the environment.  No one in the park knows this better than Chief Ranger Tim Reid, who worked his way up through the agency in the 1980s partly in hopes of landing a gig that would pay him to rock climb. After achieving that goal at Rocky Mountain National Park and Yosemite, Reid ended up as a ranger at Old Faithful before becoming Yellowstone's chief ranger. He's sympathetic to kayakers, but also understands the pressures on Yellowstone.

"There are more and more activities," he says, leaning back in a swivel chair in his office in Mammoth Hot Springs. "Then there are … derivative spins on core activities. I think it's great. (But) our charter is not to accommodate everything that comes down the pipe."

For a new activity to be considered in Yellowstone, Reid explains, park managers must first be convinced that it deserves their attention: It has to "prove that it belongs" and won't impact resources, values or public interests in the park. Then it's analyzed, potentially subjected to environmental review and opened for public comment, a process that can take years. Snowmobiling proponents know this process well – their decades-long legal battle to maintain winter access to Yellowstone recently culminated in a new winter-use plan (see The Latest, far left).

Other parks have also been challenged by adventure-sport enthusiasts. In 1999, five BASE jumpers in Yosemite staged a jump off El Capitan in hopes of demonstrating their sport's safety. One died, and another declined to make the leap. BASE jumping remains illegal in Yosemite and in most other national parks.

The diversity of recreational policies in parks can be frustrating for visitors who don't understand why their sport is any less deserving than the next. Montana State University professor and kayaker Jerry Johnson speculates that Yellowstone's kayaking ban might have more to do with economics than the challenge of managing a new activity. Towns like Cooke City, Mont., are dependent on snowmobilers' tourist dollars, he notes, while kayakers' economic impact is so small it's barely noticeable.