ATHABASCA, or Athapescow, a river in the northwestern territory of British North America, which flows into a lake of the same name. It rises in the Rocky Mountains, and has a long and tortuous course in a northeastern direction, during which it receives the Lesser Slave River, the Red Deer, and several others. The lake is about 230 miles in length, with a breadth varying from 30 to 14 miles, lying in a direction almost E. and W., in lat. 59° N., long. 110° W. It communicates with Hudson’s Bay on the one hand, and with the Polar Sea on the other.