Atlin Lake is a lake in northwestern British Columbia and is that province's largest natural lake, covering 300 sq mi (780 km2). The northern tip of the lake is in Yukon, as is Little Atlin Lake. However, most of the lake lies within the Atlin District of British Columbia. Atlin Lake is considered the source of the Yukon River although it is drained via the short Atlin River into Tagish Lake.
The name comes from Áa Tlein (in Canadian spelling Â Tłèn), the Tlingit name meaning simply "big lake".