What is ballast water?
Ballast water, not to be confused with bilge water, is water taken up or released by a vessel to alter the draft, change the trim or regulate stability. Ballast water can be sea water (salt water) or river/lake water (freshwater) depending on where a vessel is when ballasting. Ballast water is generally taken up when little or no cargo is on board. The weight of the ballast water is what helps provide stability for vessels during ocean transit. Ballast water is then generally discharged when cargo is taken on board.  Ballast water includes associated sediments that are found either in the water column or settle out in tanks. The majority of modern vessels have tanks that are specifically used to carry/hold ballast water when necessary.

Are aquatic invasive species (AIS) the same as exotic species or introduced species?
Yes. Many names exist to describe animal, plant, and bacterial species that have been moved, by human activities, to locations where they do not originally occur. AIS refers specifically to aquatic species, but in general, non-native species may be referred to as exotic, invasive, introduced, nuisance, or alien species. Alternatively, a native species is one that is found naturally in a given habitat or region.

Are all AIS harmful?
No, but this is a bit of a tricky question. Some AIS species such as the Zebra mussel (Dreissena polymorpha) in the Great Lakes create both significant economic and ecological impacts in a region. Some AIS may not have any economic impacts to humans, but they may pose a significant threat to ecological systems. Alternatively, an AIS may not appear to cause any observable economic or ecological impact. In this care, scientists must investigate many types of organisms at many levels within a food web (trophic levels) to make sure that simply because we cannot see an obvious impact does not mean that there is not an impact occuring.

How do AIS move from one region to another?
In the aquatic world, the majority of non-native species are transported by ballast water in the hulls of ships or as fouling organisms. Fouling organisms are animals or plants that attach or cling to a vessel's hull, water intake valves and associated piping, or to anchors and other equipment. When ballast water is released in port regions or when fouling organisms fall off of vessel hulls and associated equipment, some of those released animals, plants, or bacteria may begin to grow and reproduce in the new habitat. The species that successfully survive and reproduce in a new habitat are then called AIS.

AIS may also be moved by mechanisms or vectors other than ballast water or vessel fouling. AIS may be introduced accidentally through aquaculture, through the aquarium or pet industry, or by the live seafood and bait trade. Organisms that were intentionally released historically for food or ornamental purposes are also considered invasive species.