Several people reported seeing a rainbow sheen on the surface of the water several miles long just off the coast of Louisiana, to the National Response Center.
Officials have confirmed there is a five-mile wide spill of some substance in the Gulf of Mexico, but have not yet identified it.
© Jerry Moran, Native Orleanian Fine PhotographyAnother slick? Several people have reported seeing a rainbow sheen on the surface of the water several miles long just off the coast of Louisiana
An airplane is also expected to fly over the area to give officials a better idea of what's in the water.
Pollution investigators and a helicopter crew are following up on two calls to the National Response Center - the federal point of contact for reporting oil and chemical spills - Paul Barnard, an operations controller for Coast Guard Sector, New Orleans, told the Times-Picavune.
© Jerry Moran, Native Orleanian Fine PhotographyHazard: Dolphins can be seen swimming in the oil-coloured ocean. The U.S. Coast Guard is investigating the claims and has taken samples of the water
But another caller estimated the area was around 100miles long.
'We haven't been able to verify that, and it would be very unlikely for an individual to be able to observe a 100-mile long sheen,' Barnard added.
© ReutersEnvironmental disaster: The BP oil rig exploded almost a year ago on April 20, killing 11 workers and injuring 16 others
© Getty ImagesPollution: Workers clear off some of the oil washing on to Fourchon Beach from the Deepwater Horizon oil spill in the Gulf of Mexico in July last year
'They were doing some dredging at the mouth of the river, so it could be some silt or dredging material,' he said.
The BP oil rig exploded almost a year ago on April 20, killing 11 workers and injuring 16 others.
It caused 4.9million barrels of oil to gush into the Gulf of Mexico in what is now considered the second largest environmental disaster in U.S. history.
First, it was 100 miles long, then 30, NOW 5; soon it will just Obamanibly DISAPPEAR!