The map below shows distribution of the zebra mussel, an "exotic" (non-native) species that reproduces in huge numbers and causes damage to native North American mussels and clogs pipes at water treatment plants. The zebra mussel is originally from Europe and has been introduced to North American waters by hitching a ride on the hulls of ocean-going ships. (To learn more about zebra mussels, visit the Zebra Mussel Page at Wayne State University's web site, which is the source of the map below.)

QUESTION: By looking at this map and comparing it to previous map quizes showing major North American waterways--especially quiz #5--what major river systems has the zebra mussels traveled on in their conquest of North America?

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