Western Lake Erie’s harmful algal bloom is back for another summer. NOAA’s monitoring shows the season’s bloom began forming in Maumee Bay around July 12 and, like last year, has been slow to spread so far. Satellite images and field sampling confirm it is visible on the water, and as of late July the toxin levels measured in it remained low. No drinking-water or recreation advisories have been issued at this stage.
If you follow Lake Erie each summer, you have probably also seen the number attached to this year’s outlook: a “moderate” bloom, with a severity index around 3.5 on a scale where anything under 5 is considered mild to moderate. That figure is useful, but it is also easy to misread. Understanding what it does and does not mean is one of the most practical things any Lake Erie supporter can do this time of year.
What the forecast is — and isn’t
The seasonal severity forecast is an estimate of how much algae the western basin is likely to produce over the whole season. It is based largely on how much phosphorus flowed down the Maumee River in the spring. A higher number means more total bloom biomass; a lower number means less. This year’s estimate points to a bloom smaller than the worst years on record.
What the forecast is not is a beach-by-beach prediction. It cannot tell you whether a particular marina, shoreline, or swimming area will be clear or covered with scum on a given weekend. That comes down to short-term weather. Wind pushes the bloom around the lake and can pile it against one shore while leaving another clean. Calm, hot, sunny stretches let algae concentrate at the surface, and that is when toxins tend to concentrate too. Rain and mixing can break a surface scum back up.
So a “moderate” season can still produce ugly, unsafe conditions in a specific spot on a specific day — and a calmer day can clear that same spot. This year, forecasters expect the bloom to reach its peak later than usual, in the mid-to-late August through September window, running roughly three weeks behind the 2024 season.
Why it still matters
The reason the bloom returns every year is not a mystery. It is driven in large part by excess phosphorus entering the western Lake Erie watershed, much of it carried by the Maumee River. Phosphorus is an essential nutrient for growing food. The problem begins when it leaves farm fields and reaches waterways, where it feeds the cyanobacteria that form these blooms. Some of that phosphorus is “legacy” phosphorus — built up in soils over years — which means a field can keep contributing to the problem even when current fertilizer use is carefully managed.
That is why a mild forecast is good news for the season but not a reason to ease off. Real, lasting progress depends on reducing the phosphorus that reaches the lake year after year, not on hoping for favorable weather.
What’s being done
This is where practical work matters, and it is a large part of what the Lake Erie Foundation focuses on. One example is the Foundation’s Phosphorus Runoff and P-Filter Project, a partnership with Flint Run Engineering in the Maumee River watershed near Defiance. The project targets fields with elevated, legacy phosphorus and tests a filtration approach designed to capture phosphorus from agricultural drainage water before it reaches nearby streams and, eventually, the lake.
Three filters were installed in the fall of 2025, and monitoring has continued since. Early results have been promising: in project testing, phosphorus removal has exceeded 90 percent under the specific conditions measured so far. That figure reflects those test conditions rather than a guarantee for every field, and the grant-funded project is still building the evidence needed before the approach could be expanded. But it points to something important — a targeted, measurable way to address the exact source that drives Lake Erie’s blooms, while continuing to support productive farms.
No single project will solve phosphorus runoff. What the P-Filter work shows is that the problem is not hopeless, and that research can be turned into action on the fields that contribute the most.
What you can do this summer
For now, the practical advice on the water is simple: if you see thick, paint-like green scum, keep people and pets out of it, and check current conditions before heading to a specific beach or launch. The season will keep shifting with the weather.
And if you want to do more than watch the forecast, support the work that gets at the root of the problem. Learn more about the P-Filter project and help the Lake Erie Foundation move practical, science-based solutions forward.