Ships can take on ballast water in areas with water pollution or in areas where fish and plants are numerous. The water is not filtered or treated. When a ship discharges the ballast water, any pollutants, fish, or plants that survived the trip are released into the new location. If the new location is favorable, the organisms, including bacteria, fish, plants, or viruses can grow very large populations because their natural predators and diseases are absent. These aquatic invasive species cause major changes in ecosystems and cost Michigan residents millions of dollars per year to control.