Just like other freshwater mussels, zebra mussels play an important role in keeping water clean. In European waters, an individual mussel can filter 76 milliliters of water per hour. This means that zebra mussels in the IJsselmeer are capable of filtering the entire lake around two times per month, clearing up the lake considerably. Zebra mussels can also cause an enormous amount of economic damage. They attach themselves easily to exhaust pipes of power stations and cooling water systems, plugging them up. In North America in particular, they form a large problem.