The Coast Guard said Friday evening that a "very small part" of a diesel fuel and oil spill from a 73-foot workboat that sank earlier in the day has reached a Seattle beach.

Two miles of affected shoreline were surveyed, and cleaning crews have identified pockets of oil and worked to clean them as darkness fell, Capt. Scott Ferguson said.

There was no immediate word on any damage to fish or wildlife.

Oil containment boom was set out along the shoreline to try to keep any more oil from reaching the beach.

Divers also worked to plug the source of the leak, Ferguson said. The vessel reportedly has 300 gallons of diesel and 30 gallons of motor oil on board in sealed tanks. It wasn't clear how much had leaked, creating a sheen of diesel oil the size of two football fields. The sheen remaining on the surface was expected to dissipate, the Coast Guard said.

Plans call for using a crane barge to lift the vessel Saturday, the agency said.

The vessel is an old World War II landing craft that was being used as a workboat with a barge at a bulkhead project in Puget Sound near the city's West Seattle neighborhood, said Diede Janel, office manager of Waterfront Construction Inc. of Seattle.

The boat was loaded with boulders Thursday and left tied to the barge. Workers arriving Friday saw it go down at about 7:30 a.m., Janel said. It sank about 200 yards off the West Seattle shoreline.

As the vessel was sinking, workers closed the fuel vents to limit pollution, the Coast Guard said. No one was injured.

Keith Landry, a company project manager, told reporters Friday evening he didn't yet know why it sank.

The company has hired a cleanup contractor, National Response Corp. Environmental Services. Booms and absorbent pads have been deployed to contain the oil and a skimmer was brought in, the Coast Guard said.

The oil spill hasn't been catastrophic, said Katie Skipper, spokeswoman for the state's Ecology Department.

Any oil spill causes environmental damage, the Coast Guard said.