The Houston Ship Channel, one of the country’s busiest seaports and the gateway for crude oil deliveries for more than 10 percent of U.S. refining capacity, was shut down for a third day on Monday as crews continued to clean up an oil spill.  

The Houston Ship Channel shut down Saturday after a bulk cargo ship, Summer Wind, and a Kirby Inland Marine oil barge collided, spilling about 168,000 gallons of residual fuel oil and injuring six crew members. The channel, which empties into the Gulf of Mexico, gives oil barges and cargo ships access from the Gulf Coast further inland to terminals and refiners.

Channels to Houston, Texas City, Galveston and the Intracoastal Waterway remain shut. As of about 7 a.m. CDT, 43 ships were waiting to leave the port of Houston and 38 were waiting to enter, the U.S. Coast Guard said. A warning issued by the Coast Guard on Sunday said the channel might not open until the end of the week or later. About 80 vessels pass through the channel on a normal day.

The barge was carrying about 900,000 gallons of heavy oil. Cleanup crews pumped the remaining fuel oil from the barge, which has been moved to a shipyard near the accident site, according to a statement from Texas Gov. Rick Perry’s office.

Environmental groups say the region has an important shorebird habitat, with tens of thousands of wintering birds in the area this season. The Texas General Land Office deployed a bird rehabilitation trailer to the area, and the fewer than 10 oiled birds that had been found as of Sunday afternoon will be transferred to a wildlife center.

Exxon Mobil Corporation (NYSE:XOM) told Reuters Sunday that the closure has not affected its operations in Baytown, Texas, the second-largest refinery in the U.S. If the shutdown is prolonged, fuel prices could briefly rise. 

The Coast Guard and National Transportation Safety Board are still investigating what caused the crash and spill. About 24 vessels are working on skimming the oil out of the water.