Abstract: A method and apparatus for controlling zebra mussels in the inlet cell of a utility power plant by isolating a batch of water in the cell from the water supply of a lake or river and the equipment plant by shutting an inlet gate and shutting outlet valves from said cell. The batch of isolated water is thereafter heated to a lethal temperature which is maintained for a sufficient period of time to ensure 100 percent mortality to the zebra mussels within the cell. The water may be maintained in a static condition and heated by a heat exchanger disposed within the cell. Alternatively the water may be fed to a heat exchanger, heated outside the cell, and returned to the cell. The water is heated to a range of approximately 95.degree. F. to 100.degree. F. and held at the heated temperature within the cell for approximately 30 minutes.