Due to nutrient pollution, Lake Erie is at the highest risk of being affected by harmful algae blooms (HABs).

The main source of Lake Erie's vulnerability to harmful algae blooms (HABs) among the Great Lakes is nutrient pollution, particularly from phosphorus-containing agricultural runoff. These extra nutrients promote the growth of algae, which can lower water oxygen levels, endanger aquatic life, and produce hazardous conditions. The Lake Erie HABs have grown to be a serious environmental issue impacting human health, fishing businesses, and water quality. HABs still threaten the lake's ecosystem and the populations that depend on its resources, despite continuous efforts to reduce nutrient contamination through improved farming practices and wastewater management.