(CNN) - Some kind of substance has been found in the waters of the Gulf of Mexico, near where the oil spill was capped more than two years ago.

The Coast Guard says the substance is not oil.

It was found during an exploratory mission at the sunken Deepwater Horizon Platform wreckage.

The explosion there in 2010 resulted in oil sheen on the water.

Nobody knows what this substance is that was found near there, but officials say tests will be done on it.

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