The forecast for Colorado’s 2019 whitewater rafting season: Rad, thanks to epic snowfall this winter that will likely spell swift-moving rivers. International scale of river difficulty Class I: Moving water, riffles, small wavesClass II: Easy rapids, waves, clear channelsClass III: Large waves, obstacles, narrow passagesClass IV: Long rapids, unavoidable waves, many obstaclesClass V: Violent rapids, extremely difficult, unseen hazardsClass VI: Unpredictable, dangerous, nearly impossible to run Colorado’s rivers go from wild to mild as the season progresses.