Have done two day trips, both over 20 years ago. The first was from Hells Canyon Dam down to Pittsburg Landing and back, definitely the most exciting for whitewater. Can't remember the outfitter. The second one was with Snake Dancer Excursions from Lewiston up and back, not all the way to the dam thou, did switch to a smaller boat to go above the ranch
museum on the Idaho side, can't remember the name. Both were fun trips, and yes it was hot, but the water was cold.