Alsek River is a wilderness river flowing from Yukon into Northern British Columbia and into Alaska. It enters the Gulf of Alaska at Dry Bay. Most of the Alsek River's basin is within protected wilderness areas and National Parks. The Alsek and its main tributary, the Tatshenshini River, are part of the Canadian Heritage Rivers System and a UNESCO World Heritag…Alsek River is a wilderness river flowing from Yukon into Northern British Columbia and into Alaska. It enters the Gulf of Alaska at Dry Bay. Most of the Alsek River's basin is within protected wilderness areas and National Parks. The Alsek and its main tributary, the Tatshenshini River, are part of the Canadian Heritage Rivers System and a UNESCO World Heritage Site.