For the second time, a floating crane broke loose from its tethers Wednesday and drifted from the Highway 520 bridge project toward waterfront homes on Lake Washington.

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For the second time, a floating crane has broken loose from the Highway 520 project and drifted toward waterfront homes.

The piece showed up early Wednesday and was approaching residential docks north of the construction site, said a homeowner in the Laurelhurst neighborhood north of the job site, in a 4 a.m. message.

But the equipment ran aground offshore in shallow water and was retrieved, according to Emily Durante, a project spokeswoman for the Washington State Department of Transportation (WSDOT).

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A similar breakaway occurred Sept. 29, 2013, when a crane nearly hit a residential dock. After that mishap, contractors and WSDOT promised to set stronger pilings to cinch the cranes to the silty bed of Lake Washington, which is up to 200 feet deep.

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But during a windstorm Wednesday, a small barge carrying the crane dislodged. The outer frame of the barge is fastened to long pilings that protrude above the water’s surface. When winds pushed the barge sideways, the motion wiggled at least one piling, breaking it loose along a ledge where the lake bottom abruptly slopes and deepens, officials said.

The cranes are helping to build fixed spans near Foster Island, to open for east-west traffic this fall, so the old 1963 bridge decks alongside can be demolished and replaced.

Flatiron West, the contractor for this $200 million phase of the $4.6 billion megaproject, “is reassessing what their backup plan is” to restrain equipment if underwater connections fail, Durante said.

Another set of fixed spans will be built alongside, in a new contract to begin next year. The floating part of the Highway 520 bridge was completed last spring.