Only one of the barge’s oil tanks was breached, causing the approximately 168,000 gallons to leak into the water, the Coast Guard said. It was an amount seen as moderate by industry and environmental experts.

But the spill occurred along a migratory route for birds at a time of seasonal migration, which added to its environmental concerns. Wildlife officials confirmed reports received Sunday of oiled birds, some dead, in the area of the spill on East Beach, Bolivar Flats and the Texas City Dike. More than two dozen birds were discovered on Bolivar Flats, and three ducks and a loon were being rehabilitated, said Lt. Sam Dannus, a spokesman for the Joint Information Center of the Unified Command, a coalition of federal, state and local authorities involved in the cleanup.

The key to possible damage lay in how fast the oil could be recovered and removed. It was unclear how long the cleanup would take, but the Coast Guard released a bulletin to mariners on Sunday saying parts of the Houston Ship Channel, near the site of the spill, could be closed for a week or until the spill was cleared.

The Galveston-Port Bolivar ferry was shut down on Sunday.

The Coast Guard said it received a call around 12:35 p.m. on Saturday reporting a collision between the barge and a 585-foot bulk carrier ship, the Summer Wind. A tugboat named the Miss Susan was towing the barge to the Bolivar Peninsula from Texas City.

All six crew members aboard the Miss Susan were in stable condition, the Coast Guard said on Saturday.