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Lake Union

Lake Union is a freshwater lake completely within the Seattle, Washington city limits. A glacial lake, its basin was dug 12,000 years ago by the Vashon glacier, which also created Lake Washington, and Seattle's Green, Bitter, and Haller Lakes.

Part of the Lake Washington Ship Canal system, water flows into it from Lake Washington through the Montlake Cut, and out the Fremont Cut on its way to Puget Sound. Before construction of the canal, Lake Union emptied into Salmon Bay via a creek which followed roughly the same course as the Fremont Cut does today.

Because of the connection via the Hiram M. Chittenden Locks to the salt water of Puget Sound, there is some saline contamination, which worsens in the summer as the inflow rate from Lake Washington decreases and the locks open more frequently for pleasure craft.

Area of lake 580 acres 2.3 km²
Area of drainage basin 384,000 acres 1,554 km²
Volume 20,000 acre-feet 25,000,000 cubic meters
Depth (mean) 34 feet 10 m
Depth (max) 50 feet 15 m