Two and a half years after the Deepwater Horizon rig exploded and sank in the Gulf of Mexico, more oil apparently from BP's (NYSE: BP) Macondo well has been found about 50 miles off the coast of Louisiana.

"The sheen is not feasible to recover and does not pose a risk to the shoreline," according to a government press release from Wednesday. "The exact source of the sheen is uncertain at this time but could be residual oil associated with wreckage and/or debris left on the seabed from the Deepwater Horizon incident in 2010."

The Deepwater Horizon disaster killed 11 crew members and leaked some 5 million barrels of oil into the Gulf of Mexico.

BP reported the latest sheen to the National Response Center on Sept. 16. A Notice of Federal Interest was issued to BP and Transocean (NYSE: RIG) -- which owned the Deepwater Horizon rig -- informing them that they "may be held accountable for any cost associated with further assessments or operations related to this sheen."

BP said it has no reason to believe the well is leaking.

In a statement, BP said samples from the sheen reveal "alpha-olefins," which are found in the drilling mud, but not the source oil, indicating the sheen is coming from Deepwater Horizon debris. "The size of the sheen, its persistent point of origin and other factors indicate the most likely source is the bent riser pipe that once connected the rig to the well head, where a mix of oil, drilling mud and seawater were trapped after the top kill operation," said a company statement.