an apparatus for the removal or inhibition of underwater growth on an elongate submerged body . it includes at least one collar adapted to extend loosely around the elongate submerged body . the collar includes a breaker device to apply impact force on the underwater growth to break it up . the breaker device includes a voluminous body into which ambient water flows in and out . the device can advantageously include rollers . the apparatus on a smaller scale can act to inhibit the settlement of new underwater growth .