Complex sentence: Many of the film's whitewater scenes were filmed on the Kootenai River in Montana; others were filmed on the Ruby Horsethief section of the Colorado River, the Rogue River in Southern Oregon, and the Middle Fork of the Flathead River.
Split into simpler sentences: Many of the film's whitewater scenes were filmed on the Kootenai River in Montana. Additional ones were filmed on the Ruby Horsethief section of the Colorado River, the Rogue River in Southern Oregon, and the Middle Fork of the Flathead River.