Lake Washington - Canals and Bridges

Canals and Bridges

Before construction of the Lake Washington Ship Canal in 1916, Lake Washington's outlet was the Black River, which joined the Duwamish River and emptied into Elliott Bay. When the canal was opened the level of the lake dropped nearly nine feet (3 m). The canal to the Puget Sound became the lake's sole outlet, causing the Black River to dry up and disappear.

Concrete floating bridges are employed to span the lake because Lake Washington's depth and muddy bottom prevented the emplacement of the pilings or towers necessary for the construction of a causeway or suspension bridge. The bridges consist of hollow concrete pontoons that float atop the lake, anchored with cables to each other and to weights on the lake bottom. The roadway is constructed atop these concrete pontoons. Three floating bridges cross Lake Washington: the Evergreen Point Floating Bridge (officially the Governor Albert D. Rosellini Bridge - Evergreen Point) carries State Route 520 from Seattle's Montlake neighborhood to Medina while the Lacey V. Murrow Memorial Bridge and the Third Lake Washington Bridge (officially the Homer M. Hadley Memorial Bridge) carries Interstate 90 from Seattle's Mount Baker neighborhood to Mercer Island. The East Channel Bridge carries Interstate 90 from Mercer Island to Bellevue. The Evergreen Point, Lacey V. Murrow, and Third Lake Washington bridges are the longest, second longest, and fifth longest floating bridges in the world, respectively.

Many questioned the wisdom of concrete floating bridge technology after the sinking of a portion of the Lacey V. Murrow bridge on November 25, 1990. However, a Washington State Department of Transportation (WSDOT) investigation revealed that that incident resulted from the improper handling of hydrodemolition water being used during bridge renovations, rather than in any basic flaw in the bridge's concept or design. Concrete floating bridges continue to remain a viable means for the conveyance of vehicle traffic over Lake Washington.

In 1950, approximately one year after the tolls were removed from the Murrow bridge, the inland ferry system on the lake came to an end, having operated since the 1880s.