Ever since it exploded on April 20, 2010 — killing 11 crew members — BP's Deepwater Horizon oil rig has been a rotting carcass submerged in the Gulf of Mexico. In related news, the Coast Guard announced tonight that a mysterious substance is leaking from the wreckage and nobody knows what it is:

An "unidentified substance inconsistent with oil" is emitting from several areas of BP's Deepwater Horizon rig wreckage, but no sources of leaking oil were identified. That's according to the Coast Guard, which oversaw BP's recent week-long mission to inspect the undersea wells and wreckage from the 2010 explosion.

Though you would hope that any issues with the Deepwater Horizon would end right there, that's not the case. "Oil sheens" have been spotted around the spot of the rig, but no one knows what's causing those either. The Coast Guard is hoping that the two issues are connected, but won't know until lab tests on the unknown leakage are completed.

But, hey, maybe it's a coincidence. What could be causing oil slicks around an abandoned, decaying exploded oil rig? Could be anything. The Gulf's three-eyed fish must be loving their new permanent neighbor.

[via CBS News, image via Getty]