Back to Idaho Rivers Home Idaho Rivers International Whitewater Classification • Class I: Small waves, passages clear, no serious obstacles • Class II: Medium-sized waves, some maneuvering required • Class III: Numerous, high and irregular waves; scouting often required • Class IV: Powerful, irregular waves; boiling eddies; dangerous rocks; congested passages; precise maneuvering required; scouting mandatory • Class V: Difficult, violent waves; big drops; scouting mandatory and difficult; violent current • Class VI: Navigability limited; often considered unrunnable