EPA reports that the western basin is highly eutrophic and that phosphorus loading—particularly spring soluble phosphorus from the Maumee River—is a major predictor used in seasonal bloom assessment.
Bloom severity, location and toxin concentration are different measurements. A large bloom is not uniformly toxic, while a smaller concentrated patch may still warrant avoidance.
Boaters should use current monitoring rather than assuming that last week’s water appearance represents today’s route.