River flute is a flute that is held in front of the player, has open finger holes, and has two chambers: one for collecting the breath of the player and a second chamber which creates sound. The player breathes into one end of the flute without the need for an embouchure.
A block on the outside of the instrument directs the player's breath from the first chamber — called the slow air chamber — into the second chamber — called the sound chamber. The design of a sound hole at the proximal end of the sound chamber causes air from the player's breath to vibrate. This vibration causes a steady resonance of air pressure in the sound chamber that creates sound.