It was mild bloom year on Lake Erie, but upstream challenges persist

TOLEDO, OH — This year’s harmful algae bloom in western Lake Erie was among the mildest in a decade, but the improvement may owe more to favorable weather conditions than fundamental reductions in regional nutrient pollution from agriculture.

On Dec. 4, the National Oceanic and Atmospheric Administration rated the bloom a 2.4 on a 10-point severity scale, well below the long-term average. Satellite imagery showed a bloom that formed slowly in July, peaked in late August and collapsed in September.

Forecasters had predicted a 2025 bloom severity of 3 in June and the final result fell below that, spreading across about 411 square miles. It follows a stronger 2024 bloom that reached a 4.2 on the 10-point scale and spread across roughly 626 square miles.

Lake scientists say the assessme