<P> Zebra mussels are believed to be the source of deadly avian botulism poisoning that has killed tens of thousands of birds in the Great Lakes since the late 1990s . They are edible, however because they are so efficient at filtering water they tend to accumulate pollutants and toxins . For this reason most experts recommend against consuming zebra mussels . </P> <P> They are also responsible for the near extinction of many species in the Great Lake system by outcompeting native species for food and by growing on top of and suffocating the native clams and mussels . </P> <P> Zebra mussels also affect all classes of algae species, resulting in a shortage of food sources to native species of freshwater mussels and fish in the Great Lakes . </P> <P> However, zebra mussels and other non-native species are credited with the increased population and size of smallmouth bass in Lake Erie and yellow perch in Lake St. Clair . They cleanse the waters of inland lakes, resulting in increased sunlight penetration and growth of native algae at greater depths . This cleansing also increases water visibility and filters out pollutants . Each quagga and zebra mussel filters about 1 US quart (0.95 L) of water a day when confined to small tanks . In lakes, their filtering effects are usually spatially restricted (near the lake bottom) due to nonhomogeneous water column mixing . </P>

What makes the zebra mussel an invasive species