Satellite reconnaissance of western Lake Erie permitted monitoring of elevated reflectances believed to be large surface blooms of the bluegreen algae Microcystis. Although the exact causes of the blooms are unknown, several working hypotheses suggest that the recently-introduced exotic species, Dreissena polymorpha (commonly known as the zebra mussel), may promote blooms as a result of Dreissena's selective feeding and/or as a result of changes in nutrient ratios. In the most striking example, regions of high reflectance associated with Microcystis were detected in cloud-free Advanced Very High Resolution Radiometer (AVHRR) imagery of western Lake Erie on fifteen days over a six week period from August 25 to October 2, 1995. Mean reflectances in the Maumee Bay region of western Lake Erie doubled from approximately 2 percent (corresponding to seston and Secchi disk depth (SD) estimates of 1.4 mg/L and 4.9m, respectively) in early August to 4.5 percent (with seston and SD estimates of 16.1 mg/L and 0.9m, respectively) during mid-September. Estimates of the surface area of the western Lake Erie blooms ranged from 250km2 to over 1000km2. By associating satellite reflectances with Microcystis cell concentrations, AVHRR reflectance imagery provides an inexpensive means of tracking and monitoring toxic algal blooms.