It has been widely quoted in incorrect lists of facts that a duck's quack does not echo. This statement is incorrect as a duck's quack does in-fact echo.

Wikipedia defines an echo as:

A reflection of sound, arriving at the listener some time after the direct sound. Typical examples are the echo produced by the bottom of a well, by a building, or in a room, by the walls. A true echo is a single reflection of the sound source. The time delay is the extra distance divided by the speed of sound.

In tests done in an echo chamber, it was proved that a ducks quack does echo. It only takes someone to be around a cliff populated with ducks to find this out. Which leads to the most interesting question, why did the myth arise? The are a few possible explanations that could explain it are:

• The quack does echo, but it is usually too quiet to hear. When you want to hear an echo, you usually make a very loud noise to make sure the reflection can be heard. But a duck quacks too quietly, so the reflection is too quiet to hear.
• Ducks don't quack near reflecting surfaces. You need a large reflecting surface, a mountain or building for the sound to reflect off. Maybe ducks don't hang around reflecting surfaces.
• It is hard to hear the echo of a sound which fades in and fades out.