Workers try to move an oil containment boom Sunday from the shore area along Boddeker Road on the Eastern end of Galveston near the ship channel in Galveston.

TEXAS CITY, Texas — No timetable has been set to reopen a major U.S. shipping channel after nearly 170,000 gallons of tarlike oil spilled into the Texas waterway, but more help was being called in today to contain the spill and protect important shorebird habitat.

A barge carrying about 900,000 gallons of the heavy oil collided with a ship Saturday in the busy Houston Ship Channel, spilling as much as a fifth of its cargo into one of the world’s busiest waterways for moving petrochemicals, according to the Coast Guard.

Oil had been detected 12 miles offshore in the Gulf of Mexico by Sunday, and as many as 60 vessels were either waiting to get in or out. The Coast Guard — which called it a “significant spill” — said it expected to deploy more containment booms Monday, with 24 vessels working to skim the oil.

Environmental groups said the spill occurred at an especially sensitive time. The channel in Texas City, about 45 miles southeast of Houston, has important shorebird habitat on both sides, and tens of thousands of wintering birds are still in the area.

“The timing really couldn’t be much worse since we’re approaching the peak shorebird migration season,” said Richard Gibbons, conservation director of the Houston Audubon Society.

He noted that just to the east is the Bolivar Flats Shorebird Sanctuary, which attracts 50,000 to 70,000 shorebirds to shallow mud flats that are perfect foraging habitat.