Anchor cables on the Highway 520 Floating Bridge are being replaced over the next few weeks.

The Highway 520 floating bridge on Lake Washington is nearing retirement, but the state is fighting waves and winds to the bitter end.

Fifteen of the old bridge’s 58 anchor cables are being replaced this summer.

Many older cables are frayed or corroded, and could possibly snap in a windstorm, state engineers say. New pontoons are scheduled to arrive on Lake Washington in 2014, but that’s not soon enough.

“It’s only June of 2010; that’s still 4 ½ years. We could still have the storm of the century. The last thing you want would be to build the [new] bridge under duress,” said Jamie Holter, a project spokeswoman. “We absolutely cannot do without this bridge.”

At mid-lake on Tuesday, divers detached an old 2-3/16-inch diameter cable from an anchor, about 180 feet deep. A crane lifted it to the surface. A shiny new cable was attached at the lake bed, and the other end pushed through a hatch in the bridge — an exchange nicknamed “the handshake.” Two workmen in a small skiff were being rocked by small waves deflecting off the 1.4-mile concrete bridge.

The old cable was painted orange near the surface, but also displayed blisters of rust. Plant debris flaked off when the cable was lifted, and one part looked frayed. Sometimes, boats will hit a cable and tear into part of the wire strand, said bridge technician Jim Stonecipher.

Cables prevent sudden movements. The highway can rise and fall slowly to match the lake level because of hydraulic jacks inside the pontoons, to increase or release pressure on the cables.

General Construction of Poulsbo has a $4 million construction contract, and also two barges in the lake. The cables being replaced range from 18 to 33 years old. Work is expected to continue through July. Another 15 cables were recently replaced at one of the Interstate 90 floating bridges, south of the 520 bridge.

Tolling is scheduled to start next spring on the 1963-vintage four-lane 520 bridge, but that still leaves the state $2 billion short of the total $4.6 billion project cost for the entire new crossing from Bellevue to Seattle.

Mike Lindblom: 206-515-5631 or mlindblom@seattletimes.com