As much as these have caused problems they have also helped to clean up the Great Lakes, they have cleaned up Lake Mich., as well as Erie, the Small mouth and walleye, yes walleye in Lake Mich. and Erie are doing great. Lake Mich is starting to show good numbers of walleye, hopefully it will continue to grow.
Heres a little article I found.
Tom
Non-native mussels and mollusks have also caused turmoil in the food chain. In 1988, zebra mussels were inadvertently introduced to Lake St. Clair, and quickly spread throughout the Great Lakes and into many inland lakes, rivers, and canals. Since then, they have caused severe problems at power plants and municipal water supplies, clogging intake screens, pipes, and cooling systems. They have also nearly eliminated the native clam population in the ecosystem.