Water jets with pressures between 27,600 to 68,900 kPa are recommended for the removal of zebra mussels (Wong 1991). Precautions should be taken to ensure correct operation of the equipment for safety purposes and to avoid removing material other than zebra mussels. The standoff distance (mussel infested surface to tip of water jet nozzle) is important to the efficient operation of the water jet method. The greater the standoff distance, the less effective the cutting action of the water. Water jetting can be performed underwater. (Figure 6) illustrates a typical water jetting operation.