The floating bridge, designed by the engineer Homer Hadley (1885-1967), opened on July 2, 1940, to public acclaim and amazement. Many people thought that a concrete structure of this size (1.25 miles long) could never float, let alone handle traffic. At the time, The Seattle Times called it “the biggest thing afloat,” easily larger than the ocean liner Queen Elizabeth, the giant of its day. On opening day, Governor Clarence Martin called the bridge “original, distinctive, striking and graceful — a product of this great state’s vision and constructive spirit.”
The bridge, called the Lake Washington Floating Bridge or the Mercer Island Bridge, was in 1967 renamed the Lacey V. Murrow Memorial Bridge in honor of the state’s highway director. It was a marvel of engineering. Planners originally expected the bridge to carry 2,000 people a day, but from the start more than 5,000 people used the bridge on a daily basis. When tolls were taken off the bridge in 1946, this number skyrocketed.
The bridge did more than carry traffic. It turned Mercer Island from a summer resort into a suburban community. The bridge also turned Bellevue from a collection of berry and chicken farms into the fourth largest city in the state.
In November 1990, the 6,600-foot-long bridge, made of 22 floating bolted-together pontoons, was in the process of being converted from a two-way road to a one-way road. (A parallel bridge had been completed the year before, effectively doubling the amount of traffic that could cross the lake.)
The state highway department alleged that construction crews had left the pontoons’ hatches open, leaving them vulnerable to the weekend’s heavy rains and large waves. (For its part, the construction company refused to accept responsibility for the disaster, countering that “the probable cause of the failure was progressive bond slip at lapped splices in the bottom slab due to failure in bond.” It did eventually agree to pay the state $20 million, however.) For whatever reason, at midday on November 25, the center pontoons began to sink. As they disappeared under the water, they pulled more and more of the crumbling roadway down with them.
By the end of the day, the bridge was gone.
sourced – History Channel — History Link — King 5 News Seattle