Anglers need to be aware that aquatic diseases and nuisance species can easily spread from one water body to the other. For example, whirling disease, a bacterial parasite that causes deformities and death in trout, is found in many waters in Montana. In the Madison River, New Zealand mud snails are established and can be accidentally spread and invasive aquatic plants are another threat. To help prevent the spread of parasites, exotic species and diseases, follow these tips: