Aquatic nuisance species, whether animals such as the zebra mussel or plants such as curly-leaf pondweed, threaten fishing, boating, swimming, and other water-based activities. In states where they have become established, ANS have proven expensive to combat and difficult or impossible to control or eradicate. A number of them are already in our waters, but many others found in nearby states have not arrived here. With a bit preventive effort by all of us who use the outdoors, we can forestall or stop their spread to our waters.