Boats and bait buckets are suspected in the spread of zebra mussels to an additional 13 lakes in Great Lakes states and two rivers near Pittsburgh.
The government's latest inventory of the marauding mollusk has charted zebra mussel infestations in 19 states, with the largest concentrations in the Great Lakes region, where the invasion began in the 1980s.The pesky critters are but one of more than 130 foreign species that entered this country as stowaways in the ballast water of overseas ships.
Without natural predators, they have thrived and multiplied uncontrollably.
Zebra mussels cause problems for factories, local water supplies and power plants by attaching themselves to water intake pipes and quickly covering them with sharp-shelled colonies several inches thick.