A three-mile-long oil sheen off the coast of West O'ahu chased dozens of people from the beaches of Ko Olina Resort today, but did not appear to cause significant environmental damage or injuries, officials said.

The Coast Guard estimated the spill at 500 gallons and was monitoring the sheen as it moved westward late this afternoon and was trying to determine its source.

Investigators said the sheen appears to be similar to a diesel-like marine fuel that evaporates quickly, said Coast Guard Lt. John Titchen.

About 150 people using the beaches and lagoons at Ko Olina late this morning were asked to stay away from the water, Titchen said. Most then left the beach area voluntarily.

Some beachgoers in the area reported a strong smell of diesel fuel; others said they could feel a light touch of oil on their skin.

No one was injured, according to the Honolulu Fire Department.

The oil sheen was reported in the water of three of the four lagoons at Ko Olina, but had not come ashore anywhere else, Titchen said.