The 2025 western Lake Erie cyanobacterial bloom, commonly known as the summer algal bloom, was only 2.4 on the federal government’s 10-point severity index.

That made it the mildest since 2020, monitoring officials said.

It canvassed an average of 411 square miles of Lake Erie during its peak month of August, down from 626 square miles in 2024.

The seasonal assessment, issued Thursday by the National Oceanic and Atmospheric Administration, took a little longer to finalize this year because of the government shutdown, which started while the bloom was present.

“A weak bloom did persist into October before ending in late October following seasonally cooler temperatures and mixing from stronger winds,” NOAA’s assessment said. “Through the season, the bloom stayed closer to the U.S. coast,

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