Properly located flushing valves and piping arrangements which allow on-line high-velocity (3 mps) backflushing of low flow sections of pipe can be very effective in flushing zebra mussels (EPRI 1992). In areas of piping where on-line flushing is not feasible, flushing valves that allow flushing of sections of pipe during shutdown using external source of water can also be used. The backwash cycle can be designed to engage automatically for several minutes prior to the system being activated.