SALEM, Ohio — After years of troubling harmful algal blooms on Lake Erie, 2025 offered one rare bright spot: this year’s bloom was the smallest the lake has seen since 2020.
The 2025 Western Lake Erie Clonal (cyanobacterial) Bloom registered a severity index of 2.4, a level considered mild, according to the National Centers for Coastal Ocean Science at the National Oceanic and Atmospheric Administration in its seasonal assessment released Dec. 4.
In most years, the bloom is already well developed by July, spreading toxic layers across broad swaths of the lake. But this season, the bloom intensified slowly and didn’t fully establish until August. It reached its peak biomass and size in late August, then declined rapidly in early September.
A weaker bloom did linger into October, kept in check by cooler temperatures and stronger winds, but overall, 2025’s bloom stands out for how minute it was compared with recent years. Its intensity was only slightly higher than the mild 2020 bloom, the lowest on record.
Ohio farmers and farm groups welcomed the news.
“While there is work left to do, the evidence is increasingly clear that the work of Ohio farmers is paying off,” said Ohio Soybean Association President and Williams County farmer Rusty Goebel in the statement. “With the support of our partners in the State of Ohio through the H2Ohio program…we can now see the results of our efforts in a cleaner Lake Erie.”
