State officials reported tar balls and a large oil mat along the Gulf shore south of New Orleans, and the U.S. Coast Guard reported finding three oiled birds in the area on Monday.
BP spokesman Ray Melick said the area is one where BP teams were already helping with cleanup from the 2010 spill before Isaac arrived. As soon as they're given the all-clear, they will return to do more cleanup and test whether the new oil is from their spill or another source.
"There's a lot of oil out there that may not be ours," Melick said.
The area is near Fourchon Beach and Grand Isle.
The same area was heavily affected by the spill, which happened in April 2010 after an explosion aboard the Transocean Deepwater Horizon oil rig in the Gulf of Mexico. BP had contracted the rig, which had 126 workers on it, 11 of whom are presumed dead.
It's not clear whether the hurricane swept the tar balls ashore or exposed them under the sand, U.S. Coast Guard Petty Officer Bill Colclough said. In any case, he said, pollution after a hurricane is expected because the force of the storms can bring oil and other debris to the surface.
Certain areas are still closed to recreational and commercial fishing because of the BP spill, state officials said..
People on Grand Isle said they were hopeful Isaac would stir up the waters and move leftover oil out of the area so it could help revive the fishing waters off the coast.