Abstract: An acoustic device for forming a wall of sound underwater. Walls of sound are useful in water for guiding fish away from areas. Hitherto, systems have used bubbles of water to facilitate the speed of travel of the sound. Those systems have suffered from the ability to maintain a consistent wall of bubbles and have often been inefficient. The present invention seeks to provide an acoustic device for forming a wall of sound underwater and comprises a transducer connected to an acoustic waveguide. The waveguide comprises one or more projections, whereby sound generated by the transducer travels along the projection or projections to form the wall of sound. The waveguide may typically comprise compressible projections formed from neoprene. These projections are arranged in a fan or frond shape. In addition or alternatively, the projections may be laminar. The projections could be of different lengths.

Abstract: In order to deter underwater animals from an underwater region such as adjacent the entrance to an offtake pipe or channel from a river, sound and light are produced by sound and light producing units in the underwater region and are intermittently pulsed and/or at least one characteristic of the sound and light is repetitively modulated. At least some of the pulses of light and/or the occurrences of at least one feature in at least some of the light modulation repetitions are substantially synchronised with at least some of the pulses of sound and/or the occurrences of at least one feature in at least some of the sound modulation repetitions. For example, the sound may be frequency modulated, and the light may be pulsed when the sound frequency reaches its minimum. It is believed that this synchronisation of light and sound has a synergistic effect.