A concentrated oil burn in the Gulf of Mexico, conducted in May 2010 (Pic by Deepwater Horizon Response, via Flickr) Sightings of a very large sheen of oil in the Gulf of Mexico have had coastal residents and fishermen worried for over a month. But in a statement issued yesterday, the Coast Guard says the sheen is not from BP’s now-capped Macondo well, which caused harm to both Florida’s environment and economy last year. Though the Coast Guard said video footage of BP’s Macondo well shows no new leakage, the company hasn’t been ruled out as a source of the sheen. In its statement, the Coast Guard floats the possibility that oil may be emanating from a riser pipe of the Transocean rig, whose explosion led to last year’s disaster