Yet another Idahoan weighing in. I climb, but have turned down any and all river experiences here, even guided raft trips. Scares the shit outta me, lol! I'm willing to try mixed climbing (ice!), too, so nuts enough.
However, Boise (and Idaho, of course) has heaps of WW folks. Dunno where you are, but there are a lot of classes offered here, including through the local University outdoor program. They have rentals, too. We also have a whitewater park right downtown, and I'm guessing our City Parks and Rec department has classes Ask around, if there's water to play on, near you, someone offers instruction.
I've also heard of far more drownings than rock, or even "hiking" (falling off a cliff) mishaps, and I've been in Boise since 1980. Probably because water isn't considered extreme, somehow, especially if it's a paid trip, and far more people do that than go rock climbing.
There are folks here who kayak through the winter, unless it's iced over entirely. Some have even hauled kayaks up back country and snow kayaked. Boredom is the true mother of invention!
Best to you! Helen