Why do scientists use sound waves in water?

[nitharsanman]

Why do scientists use sound waves on water? And also can you provide some examples of applications of sound waves on water, for ex. submarines.

 

[FredGarvin]

This article does a pretty good job explaining things as well as giving examples.

http://en.wikipedia.org/wiki/Sonar

 

[capnahab]

Being an old sailor, sound moves faster in water due to its density and the pressure wave is much stronger for the same reason.

 

[lifeson22]

Wales use sound waves to *see* obstacles, from rock formations to prey. An obstacle will reflect the sound wave back, which tells them something's ahead. You can find reports on the connection between disoriented whales and underwater *sound pollution* due to vessels.
Scientists can use underwater sound techniques for the same purpose. But there are many other reasons you'd want to use them. It can tell you about the properties of the water, and of the materials it reflects off of.