A system for enhancing the separation of particles or fluids from water is disclosed. A settling tank or skim tank is provided with an open submersible acoustophoretic separator. In a skim tank, the separator captures and holds oil droplets or particles, permitting them to coalesce until they are large enough and have sufficient buoyant force to float to the top of the tank. In a settling or sediment tank, separator captures and holds particles until they are large enough that the force of gravity causes them to settle out of the water. The acoustophoretic device thus speeds up separation of the particles or droplets from the water.