Brooks Range, Alaska Whitwater Rivers Atigun/Sagavanirktok Class III-IV - 36 miles long (Dalton Highway Bridge to Slope Mt. Road Camp) North Slope Borough Borough Firth River Class III-IV - 99 miles long (Margaret Lake to Beaufort Sea) North Slope Borough Nigu River Class I-II - 60 miles long (Gates of Arctic National Park) North Slope Borough