The Sea Organ (Morske orgulje) is an architectural sound installation designed by Croatian architect Nikola Bašić and inaugurated in 2005 on the waterfront of Zadar, Croatia. It is a passive, site-specific instrument that produces sound through the natural motion of the sea.

The system is composed of thirty-five polyethylene pipes of varying lengths and diameters, carefully tuned to specific diatonic chords. The pipes are embedded horizontally into the structure, each connected to a resonant cavity — a sealed chamber that amplifies the air pressure variations generated by the movement of the sea.

The mechanism relies solely on the motion of the Adriatic Sea. As waves lap against the submerged openings of the organ, they push columns of water into the lower part of the system. This in turn compresses the air within the connected pipes, forcing it through narrow slits that function much like the mouthpiece of a traditional pipe organ. As the compressed air escapes into the upper chamber, it produces a tone that resonates in the cavity above. No electronics or motors are involved; the instrument is entirely passive, activated only by the sea's own energy.

The result is a continuous, organic soundscape shaped by the rhythms of the sea itself. The organ produces a low, meditative drone interspersed with airy tonal bursts. Because the instrument responds directly to the sea's behavior, the sonic output is ever-changing: soft and ambient on calm days, more dramatic and percussive during rougher tides. The tuning system, based on diatonic scales, ensures that the resulting harmonies are gentle and consonant, even when the sea behaves unpredictably.

I recorded using two hydraphones and two 8040 cardioid microphone with a Schneider disk.