Greenpeace said it's trailing an oil exploration vessel contracted by Russian oil company Rosneft to conduct seismic surveys in the northern Russian waters of the Barents Sea.
Seismic surveys employ air cannons to generate a map suggesting where reserves may be.
"Seismic testing is dangerous for two reasons: First, it is a further step towards reckless Arctic drilling, drilling that we know will never be safe," the advocacy group said Wednesday. "Second, the testing itself poses lethal risks to local wildlife, especially whales and other marine mammals."
The Natural Resources Defense Council said seismic surveys endanger some marine mammals because it masks the low frequencies used to communicate. Some marine mammals may lose their hearing completely, it said.
Some governments, like New Zealand, have established a code of conduct for minimizing acoustic disturbance to marine mammals from seismic survey operations. Greenpeace said the crew on the Russian vessel brushed off their concern by saying most marine mammals left the area during the surveys.
There was no comment from Rosneft.