Page "Columbia River" Paragraph 19
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The World Wide Fund for Nature ( WWF ) divides the waters of the Columbia and its tributaries into three freshwater ecoregions, naming them: Columbia Glaciated, Columbia Unglaciated, and Upper Snake.
The Columbia Glaciated ecoregion, making up about a third of the total watershed, lies in the north and was covered with ice sheets during the Pleistocene.
The ecoregion includes the mainstem Columbia north of the Snake River and tributaries such as the Yakima, Okanagan, Pend Oreille, Clark Fork, and Kootenay Rivers.
The effects of glaciation include a number of large lakes and a relatively low diversity of freshwater fish.
The Upper Snake ecoregion is defined as the Snake River watershed above Shoshone Falls, which totally blocks fish migration.
It includes the mainstem Columbia below the Snake River and tributaries such as the Salmon, John Day, Deschutes, and lower Snake Rivers.
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