By using a Resonance Tube. :)
This is obviously the laboratory version of the experiment, but with a large enough tube, it can be done in a lake, too!
Each frequency needs a different resonating length. You can even try this at home; buy a small speaker which emits a certain frequency tone, submerge a pipe into water - like in the picture - and slowly change the submerged length until you find one that gives a very loud sound, which can be heard clearly. This is resonance.
Here is a video that explains the concept well. :) (There's also an additional concept of how the speed of sound is measured by this technique, but it explains the basic concept well)