A Louisiana fire chief says a substance found floating in the Gulf of Mexico appears to be weathered oil. The Coast Guard is testing the substance to confirm what it is and determine where it came from.

Grand Isle Fire Chief Aubrey Chaisson said he saw the substance up close Sunday aboard a boat and also viewed it from helicopter. He said it looked like "emulsified oil." He said the substance covered about a two to three-mile area.

Coast Guard spokeswoman Casey Ranel says the agency sent out a cutter Sunday morning to collect samples.

The Coast Guard had gotten reports of an oil sheen, but officials have not confirmed the substance is oil. Ranel says dredging had been going on not far away at the mouth of the Mississippi River, and it's possible the substance is silt dredged from the bottom.