Floating through class V whitewater and grizzly country in the shadow of Mount McKinley

Tom Evans; Mike Overcast/Class V Whitewater

Bearing witness: Prairie Creek grizzly; below, paw print on the banks of the Talkeetna

But Ursus horribilis, it turns out, is straight ahead downriver—a hulking male fishing on all fours. Moe throws his kayak sideways across the current and shouts "Hyeah! Get out of here, Bear! Hyeah!" But the six-and-a-half-foot-tall griz doesn't flinch. From the raft we join Moe's bellowing as Overcast furiously backpaddles. We hover close enough that I can see the matted clumps in the bear's shaggy, pale brown coat. Then, in one smooth motion, the bear lopes easily into the brush and is gone from sight.

Moe, 30, who has been a part-time Alaskan and kayaker since he was 11, and childhood pal Overcast have owned and operated Class V Whitewater, a rafting business in Girdwood, Alaska, that specializes in high-voltage river runs, since 1992. The Talkeetna—which, wildlife willing, our group plans to run—is one of their favorites among the countless Alaskan rivers they've paddled. Named "River of Plenty" by the Tanaina Indians because of its bountiful salmon runs, its bracingly cold water flows from the Talkeetna Glacier (100 miles southeast of Mount McKinley and 75 miles northeast of Anchorage) to its confluence with the Susitna River at the town of Talkeetna, some 85 miles to the southwest. It's famous among river rats for its 22 miles of nearly continuous, burly whitewater, but Moe and Overcast are drawn just as much to the beautifully remote landscape and the monster-size king salmon that throng its depths from late June to mid-August. The serious whitewater will last only one day of our four-day, 80-mile trip; the rest will be spent floating downriver, slapping lures into the mouths of 40-pound salmon, catching glimpses of bald eagles, more bears, and porcupines, and plain old hanging out amidst the low hills covered in wild iris, roses, sitka spruce, cottonwoods, and giant Alaskan ferns at their summertime peak.