The spill was located about eight miles from the east bank of Plaquemines Parish and cleanup efforts were under way to keep the oil from reaching shore, the Coast Guard said.
Although an investigation into the cause of the leak was under way, the Coast Guard said authorities believed an unidentified vessel struck the pipeline, which was linked with an offshore well. The Coast Guard said the well was owned by Houston-based Boise de Arc. The leak was stopped about 12:45 p.m. Sunday, the Coast Guard said.
The Coast Guard, along with two cleanup companies acting on behalf of the well's owner were working to break up the spill, officials said.
The Coast Guard was searching for the vessel believed involved in the accident.