Abstract: An apparatus for controlling the cyanobacteria comprising a floatation platform having anchor means to position said platform on a body of water, an ultrasonic generator secured to said platform and adapted to generate ultrasonic waves at below and top of said body of water, and supply means to cause said ultrasonic generator suspended at a predetermined depth to emit ultrasonic waves, of a predetermined frequency, at a predetermined power level, to sever the chemical link existing between an accessory pigment and the chlorophyll a, both present in the photosynthesis system of the cyanobacteria, as well as a method for preventing, controlling or inhibiting the cyanobacteria population in a body of water