Divers found a six-foot gash on the tanker that leaked 30,000 gallons of crude oil into the Delaware River (search), creating a 20-mile-long slick that killed dozens of birds and threatened other wildlife, officials said Sunday.

Divers investigating the listing Athos I on Saturday found holes in the underwater cargo tank closest to the rear of the vessel and in an outside ballast tank, said Jim Lawrence, spokesman for the tanker's Greek owner, Tsakos Shipping and Trading SA (search).

The company said something probably struck the tanks underwater, but the Coast Guard (search) investigation has not confirmed that, spokesman Lt. Buddy Dye said.

Two tug boats were guiding the tanker toward a dock in Paulsboro, N.J., where the Venezuelan crude oil was to be delivered to a Citgo Petroleum Corp. refinery, when the leak was discovered late Friday.

U.S. Fish and Wildlife Service officials said 50 birds were dead from the spill, 300 others were affected and fish also were threatened.

A stretch of the busy river was closed to commercial and recreational traffic while the spill was being cleaned up, although the Coast Guard hoped to allow a few commercial vessels through Sunday to deliver goods to the busy Port of Philadelphia.

Dye said more than a dozen vessels, mainly carrying oil and chemicals, were parked at both ends of the port. About a million barrels of oil normally come through the Port of Philadelphia each day.

Lawrence said Tsakos hoped to unload the remaining oil from the Athos I, which had 325,000 barrels of oil aboard in seven cargo tanks, before repairing the ship.

Acting New Jersey Gov. Richard J. Codey has said Tsakos will foot the bill for the cleanup, which he estimated will take two to three months.

Residents were still fuming about the spill, the worst on the river in nearly a decade.

"It's terrible. It's absolutely terrible. Being a resident here and seeing the impact on the wildlife, it makes me sick," said Brian Goldy, 48, who often spots hundreds of Canada geese from his waterfront home in Essington, Pa.

He said he found five geese on a grassy slab by the river Sunday, all of them blackened and unable to fly. In an effort to clean themselves, the birds appeared to be ingesting the oil, he said.