Watch Echoes (1973) Official Trailer

Filmed with a camera in a waterproof housing strapped to Greenough’s back, the sequence is composed entirely of slow-motion footage shot inside the curl of waves, edited to the 23-minute song "Echoes" by Pink Floyd. The group reportedly allowed Elfick and Greenough to use the music in their film in exchange for the use of Greenough's footage as a visual background when they performed "Echoes" in concert. This short film is known to close the documentary "Crystal Voyager" (1973).