When the zebra mussel first appeared in North American waterways, there was a pressing need to understand its habitat preferences and dispersal patterns. Armed with this knowledge, it was thought that a potential pattern for dispersal might be established. Several models have been published that predicted potential zebra mussel distribution (Strayer 1991, Padilla et al. 1996, Johnson and Pedal 1996).
Current distribution patterns can give some indication of the future spread of the zebra mussel. It can be hypothesized that zebra mussels are likely to eventually infest the western United States, but to date, the Rocky Mountains have prohibited their spread. It appears that the zebra mussels will bridge this gap in a matter of time due to the many instances where transported boats have been found to have mussels attached. Although the instances where live zebra mussels have been found at inspection stations in the western United States are few, the risk of invasion continues to be taken very seriously. The threat to western waters posed by zebra mussels and other nonindigenous aquatic species has fostered a cooperative effort by resource agencies called the 100th Meridian Initiative to prevent or slow their movement west of this meridian (Drees 1998).