Man-made sounds underwater have a harmful affect on whales, according to new research.
Scientists looked at how blue and beaked whales reacted to naval sonar - a technique used by navy vessels that uses sound to communicate and navigate in water.
The blue whales, when they were diving for food, moved away as soon as they heard these man-made sounds.
This could be dangerous for the creatures, as it could mean they don't get enough food.
When the beaked whales heard the man-made sounds they stopped hunting and moved away from the area too.
Some scientists don't want the navy to do their training in whale hotspots for this reason.
Researchers began to study the effect of sonar on whales after it was feared the technique was causing them to become stranded on beaches.
In 2005 the number of beached whales was increasing and some investigations suggested the sonar was confusing the animals, putting them in danger.
This new research cannot explain if that is the case, but it does show that whales change their behaviour around navy sonar.
The scientists say more research is still needed.
Why use sonar?
Often sonar is the only way the navy can detect ships and submarines because they cannot be seen underwater.
The British Royal Navy said it already limits its use of sonar around whales, and that the research will be taken into account in the future.
A spokesperson told Newsround: "We are committed to taking all reasonable and practical measures to protect the environment and mitigate (lesson the) effects on marine mammals. "