What are nonindigenous aquatic species?

We define nonindigenous aquatic species as a member(s) (i.e. individual, group, or population) of a species that enters a body of water or aquatic ecosystem outside of its historic or native range.

Most of the nonindigenous introductions are a result of human activities since the European colonization of North America. This includes not only species that arrived from outside of North America, which are commonly referred to as exotics, but also species native to North America that have been introduced to drainages outside their native ranges within the country. An example of the former would be the Brown Trout, Salmo trutta, a native of Europe first imported to the United States in 1883 from Germany. An example of the latter would be the Coho Salmon, Oncorhynchus kisutch, a native to the Pacific coast from northern California to Alaska, which was introduced into the Great Lakes as early as the 1920's.

The importance of studying nonindigenous organisms is to learn what effects they may have on the native organisms and the physical environment.