Enviros are attacking a plan by the U.S. Navy to use an advanced sonar system to detect submarines from potentially hostile developing nations, arguing that the use of low-frequency, high-decibel sound waves over large undersea areas could harm whales and other sea life. The Natural Resources Defense Council is threatening to sue to stop use of the $350 million sonar system under a federal law that requires the military to minimize its environmental damage. A $10 million study financed by the Navy found that the system would have no significant impact on whales, but the study authors admit there is much they don’t know about large whale species. The study authors also say that it’s unreasonable to demand that no sea creature ever be harmed by the system and that a more reasonable standard is whether an entire population or habitat would be disrupted.