The ocean is full of sound, some natural and some anthropogenic (human-made). Most anthropogenic sound comes from boat traffic, especially large shipping freighters. Other human noise contributors come from industrial activities such as drilling, mining and militaryobservations using sonar. In Glacier Bay, most boat noise is produced by small recreational boats, cruise ships, and tour boats. Other natural sounds you can hear underwater include, surf, rain, wind, underwater earthquakes, glaciers calving, fish, crustaceans, marine mammals, and more! These underwater sounds are heard and recorded by a hydrophone. Many marine animals, especially mammals, rely on sound to communicate, navigate, find food, and interact with their environment. By studying underwater sound and analyzing data, scientists are trying to understand how ambient noise, or background noise, may impact or alter the behavior of marine mammals and other ocean animals.