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The Ship Canal and Lake Union connect Lake Washington with Puget Sound. On the east, the Montlake cut connects Union Bay in Lake Washington with Portage Bay. Portage Bay connects to Lake Union, which covers approximately 581 acres and has an average depth of 32 feet. Heading west, the narrow Fremont Cut connects with Salmon Bay and the Hiram Chittenden (Ballard) Locks. The Locks allow boats to pass between the freshwater of the Ship Canal and the saltwater of Puget Sound and regulate the water level in the Lake Union/Ship Canal/Lake Washington system.
Lake Union and the Ship Canal are important areas for shipping, recreational navigation, industrial and commercial businesses, recreation, and fish and wildlife habitat. The Ship Canal and Lake Union are particularly important as migration corridors for all salmon entering and leaving the greater Lake Washington watershed.
The Ship Canal and Lake Union have a number of environmental concerns. The Locks allow saltwater to enter into the freshwater areas of the Ship Canal and Lake Union, which during warmer summer months can create aquatic areas without oxygen. The area also has high water temperatures during the late summer, which can be problematic for migrating salmon. Concentrations of fecal coliform bacteria can exceed the state water quality standard, particularly in the winter. Bottom sediments throughout the Ship Canal/Lake Union system are contaminated from ongoing urbanization and past and current industrial activities. Less than five percent of the Ship Canal and Lake Union shoreline has natural vegetation.