The Alsek River (; Tlingit Aalseix̱' ) 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. In the year 2016, the Alsek River captured the flow of the Slims River due to the retreat of Kaskawulsh Glacier. Researchers attributed the change in flow to human-caused climate change; this was the first time human-caused climate change was implicated in the reorganization of a river. Research indicates that in a few decades, Alsek River may further change its final course. The rapidly retreating Grand Plateau Glacier separates Alsek River and lake from nearby Grand Plateau Lake. Geologists predict that when the two lakes merge, Alsek River will abandon its current outlet in favour of the steeper way to the ocean through Grand Plateau Lake and a small embankment, moving its outlet some 17 miles (28 km) to the southeast, within the confines of Glacier Bay National Park. Course The Alsek starts at the confluence of the Dezadeash River and Kaskawulsh River in Kluane National Park and Reserve. After flowing south into the northwestern tip of British Columbia, it is joined by the Tatshenshini River in Tatshenshini-Alsek Park. Finally after passing through the glacier-fed Alsek Lake, it reaches the Pacific Ocean at Dry Bay, in the Gulf of Alaska, south of Yakutat, Alaska, close to the northern end of the Alaska Panhandle. Although the river is navigable by kayak or rubber raft in its northern reaches, it rapidly becomes unnavigable—for any but the most experienced and skilled kayakers—at Turnback Canyon. On older maps, the Alsek river is labeled as the Kaskawulsh and The Tatshenshini as the Alsek. Some Yukon First Nation elders also refer to the river as the Kaskawulsh. The river flows next to the Lowell Glacier which has sometimes blocked off the river and created a large lake behind it, "Neoglacial Lake Alsek." The last such blockage took place in 1850; its release created a massive flood, washing away everything in its path on the way to the Pacific. The river carries a lot of silt from the Alsek lake/glacier, which contributes to the river's low temperature. The Alsek and