The zebra mussel, Eurasian watermilfoil and round and tubenose goby are all nonindigenous species thought to have been brought to the United States from Europe in the ballast water of ocean-going vessels. These vessels pick up ballast water in their homeport when they are carrying a light load and discharge it here in U.S. waters when picking up heavier loads. This water often contains small fish, shellfish and plants native to the port where the ballast water was picked up, e.g. the Caspian Sea. Since these nonindigenous species have no natural predators here, they flourish and often outstrip native plants and waterlife by competing for food and space. This can severely disrupt the normal food chain, and cause the disappearance, or severe reduction in numbers of game fish, having an economic impact on the fishing industry. Rapidly growing nonindigenous weeds that outpace native ones may provide fewer nutrients for water birds as well as fish that feed on native plants. They clog waterways and lakes, necessitating their costly removal. Once these nonindigenous aquatic species take hold, there is little that can be done to eradicate them, so authorities need to take measures to prevent their entry into American waters, and if they do manage to invade U. S. waters, then must take stringent measures to halt their spread. If these measures are not taken, these invading species may have a serious economic impact on all water-related ventures.
Nonindigenous aquatic species continue to invade waters of the great Lakes Region where they gain entry from the discharged ballast water from European vessels, and from there they have the potential to spread throughout the United States via lakes and rivers, displacing native species as they go. Having no natural predators here, they survive, and little can be done to halt their invasion. While occasionally benefits can be derived from them, such as the cleaning of polluted waters by zeb...