The Yukon River is a major watercourse of northwestern North America. From its source in British Columbia, Canada, it flows through Canada's territory of Yukon (itself named after the river). The lower half of the river continues westward through the U.S. state of Alaska. The river is long and empties into the Bering Sea at the Yukon–Kuskokwim Delta. The average flow is . The total drainage area is , of which lies in Canada. The total area is more than 25% larger than Texas or Alberta. The longest river in Alaska and Yukon, it was one of the principal means of transportation during the 1896–1903 Klondike Gold Rush. A portion of the river in Yukon—"The Thirty Mile" section, from Lake Laberge to the Teslin River—is a national heritage river and a unit of Klondike Gold Rush International Historical Park. Paddle-wheel riverboats continued to ply the river until the 1950s, when the Klondike Highway was completed. After the purchase of Alaska by the United States in 1867, the Alaska Commercial Company acquired the assets of the Russian-American Company and constructed several posts at various locations on the Yukon River. The Yukon River has a recent history of pollution from military installations, dumps, wastewater, and other sources. However, the Environmental Protection Agency does not list the Yukon River among its impaired watersheds, and water-quality data from the U.S. Geological Survey shows relatively good levels of turbidity, metals, and dissolved oxygen. The Yukon and Mackenzie rivers have much higher suspended sediment concentrations than the great Siberian Arctic rivers. The Yukon River Inter-Tribal Watershed Council, a cooperative effort of 70 First Nations and tribes in Alaska and Canada, has the goal of making the river and its tributaries safe to drink from again by supplementing and scrutinizing government data. Name The name Yukon, or ųųg han, is a contraction of the words in the Gwich'in phrase chųų gąįį han, which means white water river and refers to "the pale colour" of glacial runoff in the Yukon River. The contraction is Ųųg Han, if the /ųų/ remains nasalized, or Yuk Han, if there is no vowel nasalization. In the 1840s, different tribes had different opinions as to the literal meaning of Yukon. In 1843, the Holikachuks had told the Russian-American Company that their name for the river was Yukkhana and that this name meant big river. However, Yukkhana does not literally correspond to a Holikachuk