NEW ORLEANS September 5, 2012, 07:03 pm ET

NEW ORLEANS (AP) — Waves from Hurricane Isaac uncovered oil previously buried along Gulf Coast beaches, exposing crude that wasn't cleaned up after the BP spill in 2010.

Since Isaac made landfall more than a week ago, the water the storm has receded and tar balls and oil have been reported on shores in Alabama and Louisiana, where officials closed a 13-mile stretch of beach Tuesday.

BP said Wednesday some of that oil was from the spill, but said some of the crude may be from other sources, too.