TEXAS CITY, Texas (AP) — The cleanup of an unknown amount of thick, sticky oil that spilled into the Galveston Bay blocked the movement Sunday of about 60 ships, including three cruise ships, between the Gulf of Mexico and one of the world's busiest petrochemical transportation waterways.

A barge carrying nearly a million gallons of marine fuel oil sprung a leak after colliding with a ship Saturday afternoon in the Houston Ship Channel. Officials believe only one of the barge's tanks — which holds 168,000 gallons — was breached, though Coast Guard spokesman Lt. Sam Danus said Sunday it wasn't clear how much oil had spilled.

Crews were skimming oil out of the water Sunday and about six and half miles of containment booms were being used to protect environmentally sensitive areas, the Coast Guard said. The area is home to popular bird habitats, especially during the approaching migratory shorebird season. Danus said flights are planned later Sunday to assess whether wetlands or wildlife had been affected.

While the remaining oil in the damaged barge is removed Sunday, the mouth of Houston ship channel is closed to all ships in either direction. It's not clear when it will reopen, Danus said. Twenty-seven vessels, including two cruise ships, are waiting to enter the channel from the Gulf of Mexico. Thirty-four vessels, including one cruise ship, are waiting to leave Galveston Bay.

Also closed is the Texas City dike, a popular fishing spot that goes out into the Gulf for a few miles. Lee Rilat, 58, owns Lee's Bait and Tackle, the last store before the access road to the dike, which was blocked by a police car on a breezy, overcast Sunday. If it weren't for the spill, Rilat's business would be hopping.

"This would be the first spring deal, the first real weekend for fishing," Rilat said. He says ships and barges have collided before, but this is the first time — at least this year — that someone has sprung a leak. His wife, Brenda Rilat, said sea fog was hanging over the bay Saturday.

Rilat, who's lived in the area most of his life, doesn't think the spill is too big of a deal. "It'll be fine. ... Mother Nature takes care of its own," he said.

The collision in the channel, which sits between Galveston Island and Bolivar Peninsula, was still being investigated, the Coast Guard said. Once the oil is removed from the damaged barge, it will be taken to a local shipyard to be assessed, Danus said.

The captain of the 585-foot ship, Summer Wind, reported the spill just after noon Saturday. Six crew members from the tow vessel, which was going from Texas City to Bolivar, were injured, the Coast Guard said.

Kirby Inland Marine, which owns the tow vessel and barge, is working with the Texas General Land Office and many other federal, state and nonprofit agencies to respond to the spill, The Coast Guard said. Tara Kilgore, an operations coordinator with Kirby Inland Marine, declined to comment Saturday.

Jim Suydam, spokesman for the Texas' General Land Office, described the type of oil the barge was carrying as "sticky, gooey, thick, tarry stuff."

"That stuff is terrible to have to clean up," he said.

Richard Gibbons, the conservation director of the Houston Audubon Society, said there is important shorebird habitat on both sides of the ship channel. One is the Bolivar Flats Shorebird Sanctuary just to the east, which Gibbons said attracts 50,000 to 70,000 shorebirds to shallow mud flats that are perfect foraging habitat.

"The timing really couldn't be much worse since we're approaching the peak shorebird migration season," Gibbons said. He added that tens of thousands of wintering birds remain in the area.

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Associated Press writer Terry Wallace in Dallas contributed to this report.