The zebra mussel Dreissena polymorpha and quagga mussel Dreissena rostriformis bugensis, two species of invasive bivalve mollusks, pose an economic risk to the Columbia River Basin (the Basin), but there is a large range in the forecasts of potential economic costs. This report documents the potential economic implications of a widespread zebra or quagga mussel (mussel) infestation in the Basin. We emphasize the potential effects of a mussel infestation on facilities, resources, ecosystems and species that are closely related to the Fish and Wildlife Program (FWP) and the Federal Columbia River Power System (FCRPS). The report reviews the current state of knowledge about the risk of mussel introduction, establishment, growth and densities, and estimates some potential costs of infestation, avoidance, and control. We conclude with recommendations for research and policies that could improve the assessment of the risks and costs of mussel infestation.