(CNN) A sunken Soviet nuclear submarine that's been on the sea floor for three decades is leaking an abnormally high amount of radiation, according to the Institute for Marine Research. The institute says the leak poses no risk to people or fish.

The researchers took water samples near a ventilation duct on the Cold War-era sub. They contained up to 800,000 times the normal amount of the element caesium, a metal that can be radioactive.

"The levels we detected were clearly above what is normal in the oceans, but they weren't alarmingly high," expedition leader Hilde Elise Heldal said in a media release.

The scientists used a remote-operated vehicle called the Ægir 6000 to survey the wreck, which sits about a mile below the water surface.





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