This article presents empirical evidence that the exotic zebra mussel may be altering the limnological paradigm of increasing cyanobacterial dominance with increasing nutrient enrichment by fostering dominance by Microcystis in lakes with relatively low total phosphorus. Research was conducted using samples from 61 Michigan lakes of varying nutrient levels that contain or lack zebra mussels. Results suggest negative consequences of Dreissena invasion for water quality in lakes with low to moderate levels of nutrients.