They can outcompete native species for food, space and other resources, sometimes even causing the extinction of native species. Once established, exotics rarely can be eliminated. But the outcome of an introduction is risky and complex, and the consequences are not always anticipated. Today, after decades of experience, there are laws governing the intentional introduction of non-native species. However, we also have to work to prevent the unintentional transfer of organisms.
Most introductions are the result of human activities.
There are many ways we can move organisms around the world. Cultured non-native species can also escape from captivity. The aquaculture industry is now heavily regulated to minimize introductions. The release or escape of specimens into the wild by the industry and the hobbyist aquarium owner has led to introductions. The common goldfish, for example, has become a nuisance species in eastern Washington.