If you were a blue whale, the water in most of the world’s oceans would be so murky that you wouldn’t be able to see your own flukes. Which is why most marine species use sound to navigate, feed, find mates, and communica—BLUURRRRGGGGHHHH AAAARRROOOOOO WAA WAA WAA—oh, sorry, pardon the interruption.

That’s just the noise of whales cheering. See, they just won a major noise pollution battle against the US Navy. For over a decade, the Navy has been trying to convince the courts that they can use an ultra-loud sonar array in a way that is safe for marine life. But on July 15, the Ninth US Circuit Court of Appeals in San Francisco said that no, actually it’s not safe at all.

The ruling came down to a Navy-friendly interpretation of the National Marine Protection Act, which prohibits any US citizen, agency, or organization from harming creatures like whales, dolphins, and seals. That ruling was made by NOAA’s Fisheries Service, putting them in cahoots with the Navy. However, NRDC and several co-defendants took NOAA Fisheries to court, and eventually won the case. As a result, the Navy will be barred from using its deep submarine hunting sonar in much of the world’s oceans during peacetime.

Sonar Subwoofers

The US hasn’t faced any real naval threat in decades. During the 1970s, however, the Soviet Union was developing quieter submarines. At the same time, the ocean itself was getting noisier from activities like oil drilling and marine shipping. The US Navy wasn’t just worried about a sneak attack from the deep: Submarines that creep close to an enemy’s ships or shore are capable of all sorts of clandestine shenanigans, like eavesdropping on short range communications.

So the Navy started working on a special long-range sonar tool. They called it Surveillance Towed Array Sensor System Low Frequency Active, or SURTASS/LFA. One quick aside: That is a monstrous acronym with three S’s, none of which stands for sonar! But sonar it is. The system deploys from the aft ends of special sub-hunting surface ships. Once lowered from the massive reel, the system’s 18 source projectors—basically huge, aquatic subwoofers—emit loud, low-frequency tones.

The problem is those frequencies—from around 100 to 500 hz—also happen to be the sweet spot for a lot of marine life. “It’s important to understand that the ocean is a world of sound, not sight,” says Michael Jasny, director of NRDC’s marine mammal protection project. Whales, dolphins, and porpoises use sound to find food, meet mates, avoid predators, maintain social groups, or simply navigate the wide seas. “Marine mammal species perceive these SURTASS/LFA sounds as a threat and react accordingly,” says Jasny.

In extreme cases, that means death. Low-frequency sonar has been implicated in mass whale and dolphin beachings. Or consider if one of those creatures hears the noise while diving deep. If it gets spooked and comes to the surface too fast, it will get the bends.

Less lethal, but still damaging, are effects to the mammals’ social structure. Imagine you are in a loud restaurant with a group of friends, and the person you really want to catch up with is sitting far enough away that the din makes it impossible to chat without shouting. Eventually, you give up. Okay now pretend that instead of people in a restaurant, you and your friend are whales at the opposite ends of an ocean. In the past, that’s been fine, because you’re a species that has evolved to communicate over long distances. However, this sonar gear becomes a static wall separating you from your friends. And the interference isn’t just annoying. “It can mean the difference between feeding and not feeding, or breeding and not breeding,” says Jasny.

Protecting Invisible Animals

The Navy and NOAA’s National Marine Fisheries Service actually agree with the environmentalists on that. They diverge on whether sonar-testing waters actually contain the affected mammals.

“This is not a matter of NOAA Fisheries misinterpreting the science, but of them misapplying the law,” says Jasny. The majority of the world’s oceans haven’t been surveyed, but marine biologists can predict where marine mammals will live. But NOAA Fisheries had said the Navy could use their sonar tech as long as there wasn’t direct evidence of a marine mammal in the area. Under that liberal application of the National Marine Protection Act, the Navy ended up using the array even in known biodiversity hotspots like the Galapagos Islands.

In its ruling, the court says NOAA Fisheries has to be overprotective, using precautionary ecological principles to make sure the Navy only uses the sonar array in mammal-free waters. But only during peacetime. And the Navy did not respond with a comment in time for the story as to how this may affect their peacetime operations. NRDC was a co-plaintiff in the Ninth Circuit Court case, the third time NOAA Fisheries and the Navy have been taken to court over the sonar device.

NOAA Fisheries stated they are still reviewing the ruling and its implications. Even if they do not appeal the decision (or somehow find a workaround), the new laws won’t shelter marine mammals completely. Big sonar devices like this one transmit far and wide. In the early 1990s, a group of scientists dipped an acoustic transducer into the Indian Ocean near a place called—you’ll love this—Heard Island and began broadcasting high energy, low frequency signals. Prior to this, they had set up hydrophones all over the world. The furthest spot that picked up any noise? It was over 10,000 miles away, off the coast of Washington State.