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and more on control of zebra mussels (Miller et al. 1992). The City of N[onroe, Michigan, serves as an example of how munici- palities can be adversely affected by the zebra mussel. The zebra mussel was first detected in the raw water system for the city in January 1989. By July 1989, the Lake Erie water intake for Monroe, a community of 24,000, was reduced 20% by the infestation of the mussel, and outages occurred from the winter of 1989 u~ the spring of 1990 (LePage 1993). 'The costs of control- ling the zebra mussel at this facility was estimated at about $301,000 spent between January 1989 and January 1991, about $100,000 more for 1991 expenditures, and an extra burden of additional annual operating costs that will be required as long as the facility is infested with the zebra mussel. Control measures at the Monroe facility are dependent on heavy chlorination. If this facility is required to use other, more environmentally acceptable means for control of the mussel, such as ozone treatment in lieu of chlorination, additional costs could be $3 million for a new treatment plant (LePage 1993 ). Due to its propensity to move from one location to the other, the zebra j mussel has been called the "wandering mussel". In this respect, zebra mussels di fer from other native freshwater bivalves in North America that do not have planktonic larvae. Zebra mussels colonies appear barnacle-like, but unlike barnacles, the zebra mussel can drop its attachment and undertake movements like other clams. If more desirable locations are found later, the mussel can regenerate threads and Zebra mussels can indirectly affect humans by attaching to various man- made and other substrates, but directly affect native mussels (unionids) and other animals (e.g., crayfish and turtles) by attaching to them. Mean densities of 6,777 zebra mussels attached per unionid have been reported in Lake Erie (Schlcesser and Kovalak 1991). This can lead to eventual death of host mussels, and has resulted in the decimation of native mussels in Lake Erie (Stolzenburg 1992). Zebra mussels feed by filtering plankton and other suspended matter from the water and depositing it in the form of feces and pseudofeces (Scholoessaer and Kovalax 1991; reattach. The juvenile mussels can break away from their attachments and generate new, buoyant threads that enable them to drift with the currents and find a new substrate. Adults are able to move to a new location with their muscular foot. Griffiths 1993a; Tucker et al. 1993)• An adult zebra mussel filters about 1 liter of water per day (Leach 1993), removing virtually all of the plankton from the water in the process. Zebra mussel feeding is causing physical, chemical, and biological changes in