As workers in bright yellow suits picked quarter-sized "tar balls" out of the sand along Galveston Bay on Monday, strong incoming tides kept washing more ashore.
Elsewhere, crews lined up miles of oil booms to keep oil away from the shoreline and bird habitats, two days after a collision in the Houston Ship Channel dumped as many as 170,000 gallons of oil from a barge into the water along the Gulf Coast and shut down one of the nation's busiest seaports.
With cleanup well underway, the Coast Guard said it hoped to have the channel open to barge traffic as quickly as possible but that more tests were needed to confirm the water and the vessels traveling through the channel were free of oil.
The closure stranded some 80 vessels on both sides of the channel. Traffic through the channel includes ships serving refineries key to American oil production.
Officials believe most of the oil that spilled Saturday is drifting out of the Houston Ship Channel into the Gulf of Mexico, which should limit the impact on bird habitats around Galveston Bay as well as beaches and fisheries important to tourists.
"This spill -- I think if we keep our fingers crossed -- is not going to have the negative impact that it could have had," said Jerry Patterson, commissioner of the Texas General Land Office, the lead state agency on the response to the spill.
The best-case scenario is for most of the slick to remain in the Gulf for at least several days and congeal into small tar balls that wash up further south on the Texas coast, where they could be picked up and removed, Patterson said. Crews from the General Land Office are monitoring water currents and the movement of the oil, he said.
Parts of Galveston Island, a popular tourist destination due to its beaches and parks, were closed to the public Monday. Crews have laid booms around environmentally sensitive areas.
Some black, tar-like globs, along with a dark line of a sticky, oily substance, were seen along the shoreline of the Texas City dike, a 5-mile jetty that juts into Galveston Bay across from a tip of Galveston Island.
Seawolf Park in Galveston, a popular spot for fishermen and tourists, was closed Monday after small amounts of oil were spotted in the water, manager John McMichael said.
"Anytime you shut down the park, it's going to have an economic impact," McMichael said. "How much, we don't know because we don't know how long the park will be closed."
In Texas City, near several refineries, crews picked up tar balls out of the sand and set up cannons that boomed every few minutes to scare off birds from the oil-slicked beach.
At Galveston's East Beach, workers set up metal posts to hang lines of absorbent material to collect tar balls as they washed up. On the other side of a jetty, crews were scooping oil from the sand and pouring it into plastic bags.
"It's one of those things with it being so new, it's very hard to tell how long we'll be out here," Coast Guard Petty Officer Richard Forte said.
Jim Guidry, executive vice president of Houston-based Kirby Inland Marine Corp., which owned the barge, has said the company -- the nation's largest operator of inland barges -- would pay for the cleanup.
"We're very concerned. We're focused on cleaning up," he said.
Refineries in Texas City appeared to have enough crude oil on hand to continue operating until the ship channel can re-open, Patterson said.
Environmental groups said the spill occurred at an especially sensitive time and place. The channel in Texas City, about 45 miles southeast of Houston, has shorebird habitat on both sides, and tens of thousands of wintering birds are still in the area.
At least 50 birds of six species have needed treatment due to the oil, said Richard Gibbons, conservation director of the Houston Audubon Society. The species include sanderling, ruddy turnstone and the American white pelican, Gibbons said.
Gibbons agreed that the majority of the oil could wash up as tar balls further south. If it hits the coast sooner, it could damage the natural habitat of many more birds, he said.
The spill also temporarily suspended state-operated ferry service between Galveston and Port Bolivar, affecting thousands of travelers. Ferry service was expected to resume Monday afternoon.
Two cruise ships were allowed to travel through the spill area "to minimize inconvenience" to thousands of passengers and limit the spill's economic effects, the Coast Guard said.
The channel, part of the Port of Houston, typically handles as many as 80 large ships, as well as about 300 to 400 tugboats and barges.
The barge was carrying about 900,000 gallons when it collided with a ship. The resulting accident falls far short of major American oil spills such as the 1989 Exxon Valdez disaster in Alaska, which dumped 11 million gallons of oil into the Prince William Sound, or the Deepwater Horizon spill, in which more than 100 million gallons of oil spilled into the Gulf of Mexico four years ago.
Associated Press writer Michael Graczyk in Texas City contributed to this report.