Old oil has washed up on some Louisiana beaches after Hurricane Isaac and officials are testing whether it’s left over from BP”s Deepwater Horizon spill in 2010.

Officials late Tuesday restricted fishing in waters extending a mile off a roughly 13-mile stretch of coastline.

The weathered oil was in the form of tar. The state Wildlife and Fisheries Department said there was a large mat of tar on one beach and concentrations of tar balls on adjacent beaches. An adviser to Gov. Bobby Jindal said later surveys found several more tar mats. Their size was not immediately clear.

Oil company BP PLC said it was too early to say if the tar came from oil that spewed into the Gulf of Mexico when the Deepwater Horizon rig exploded.