The Yukon River originates in the coastal mountains of Canada and flows 1,979 miles in a wide arc to the Bering Sea. The river flows northwest through Yukon-Charley Rivers National Preserve for 128 miles. The river is silt laden in summer due to glacial runoff, and it is completely clear in winter when glaciers are frozen. As the river enters the preserve near Eagle, it flows across a narrow floodplain flanked by high bluffs and heavily forested hills. The bluffs become less prominent as the river leaves the preserve near Circle.