The quagga mussel (Dreissena bugensis), a close relative of the zebra mussel (Dreissena polymorpha), was recently discovered in Lakes Mead, Havasu and Mohave on the lower Colorado River.   This infestation constitutes the first population of dreissenid mussels west of the 100^th Meridian and has the potential to increase their rate of spread in the western U.S.  First, we forecasted the potential spread of dreissenid mussels throughout the entire United States by predicting the overland movement of recreational boaters with a production-constrained gravity model.  The gravity model was based on 210 watersheds within the continental U.S.  For each watershed we estimated the number of recreational boaters, the amount of surface water, and distances between the watersheds.  Second, we used a computable general equilibrium model to determine the economic impact of a dreissenid introduction on the Columbia River basin.  Our results predict that the relative probability of a dreissenid introduction to the Columbia River Basin has increased by ~25% compared to a previously published model based on the pre-Colorado invasion situation.  Our economic analysis indicates that a dreissenid mussel invasion of the Columbia River Basin would result in a mean annual welfare loss of roughly $5 million. These results provide guidance to determine appropriate investment levels in prevention and control strategies in the western U.S.