PUT-IN-BAY, Ohio — Lake Erie and the scores of people who depend on it for drinking water, recreation and tourism should expect a “moderate” harmful algal bloom season this summer, according to the latest forecast from the National Oceanic and Atmospheric Administration.
Patches of green, toxin‑producing scum are most likely to form in the lake’s western basin starting in July, intensifying in August and persisting into September, where calm, hot days can concentrate the bloom into streaks and mats of poisoned pea soup. Whether the swill hugs the Ohio or Michigan shoreline will depend on the winds, though.
The outlook, shared June 25 during a briefing with Ohio Sea Grant and Stone Laboratory, comes as scientists see hints that years of work on land are starting to matter.
Harmful algal blooms (HAB) in western Lake Erie form when spring rains wash phosphorus off farm fields and other sources into rivers such as the Maumee, which then deliver that nutrient pulse into the lake. Once warm, calm conditions arrive in summer, cyanobacteria use that phosphorus to grow into dense blooms, some of which produce toxins like microcystin, which is known to be fatal to dogs exposed to it. Scientists continue to study the risks from long‑term, low‑level exposure in water and air.
Chris Winslow, director of Ohio Sea Grant and Stone Lab, framed both the progress and the remaining work in urgent terms.
“This is truly all hands on deck,” he said. “We have learned a lot, and we’re doing some tremendous stuff. But it is truly all hands on deck.”
At the briefing, state and federal scientists said that payoff is already starting to show up in monitoring data. Ohio’s H2Ohio‑funded wetlands, which are being tracked by a network of universities, are beginning to demonstrate that they can pull phosphorus and sediment out of water before it reaches Lake Erie.
Long‑term records from Heidelberg University’s National Center for Water Quality Research — the group that has sampled the Maumee River for decades — and new U.S. Environmental Protection Agency analyses both suggest that the dissolved form of phosphorus that supercharges algae has finally started to decline. Those improvements are showing up during big storm flows, the very events that do the most to fuel harmful algal blooms, meaning small changes on the land can have an outsized effect downstream.
But several speakers also warned that as heavy spring rains and single, intense storms play an ever larger role in washing phosphorus into the lake, the challenge to rein in harmful algal blooms will only become more daunting.
Trouble brewing
Because the Maumee is the single largest phosphorus source to the western basin, the United States and Canada agreed in 2016 to a binational target to cut Maumee and western basin tributary phosphorus loads by 40% from 2008 levels; scientists say blooms will continue to plague the lake until that reduction is actually achieved.
“We have not won this, we have not gotten to our 40% target, but we have learned a lot, and we’re doing some tremendous stuff,” Winslow said.
Last year’s bloom was mild, with a severity index of 2.4. This year, it’s expected to reach 3.5. The forecast ranks 2026 on par in overall magnitude alongside 2022 and 2024.
What sets this year apart is how and when the phosphorus arrived. Nate Manning, a research scientist at Heidelberg University’s National Center for Water Quality Research, told the audience that Maumee River sampling shows an unusually front-loaded season.
“About 75% of the total load from this spring was delivered in April, and 60% of it was from this one storm event,” he said. “Really, one big storm in April was the primary driver of loading for 2026.”
As recently as June 16, Manning said, the Maumee River had already carried about 293 metric tons of phosphorus into Lake Erie, and findings based on National Weather Service outlooks suggest that number will creep up to around 304 metric tons by the end of July, very close to 2024 and in line with the last few years.
The type of phosphorus in the water is important, too. One form, called dissolved reactive phosphorus, is the kind that really whets the algae’s appetite; the HABs make use of it right away. The other major form is phosphorus stuck to bits of soil and sediment. That “particulate” phosphorus is trending higher than expected, Manning said, likely because powerful spring flows were chewing away at stream banks and carrying extra dirt — and the phosphorus attached to it — into the river while fields were still bare.
But according to U.S. EPA scientist Cal Pueblo, even as the dissolved form of phosphorus edges down, the surge of total nutrients during heavy rains is still pushing Lake Erie toward trouble.
One very wet year, 2019, stood out to him as an example of how decisions on the land can quickly show up in the river. Fields were so saturated that spring that farmers could not apply as much fertilizer and manure as usual. Phosphorus loads were still high because of the sheer amount of water flowing into the lake, but lower than the models would have predicted, especially for the dissolved algae‑ready form. The less fertilizer that’s used on the land, the better, at least for the lake.
“Double down”
Sarah Emery, director of the Center for Great Lakes and Watershed Studies at Bowling Green State University, was on a research trip in northern Michigan and did not attend the briefing. In an interview with Farm and Dairy, she said the mix of recurring blooms and a warming, stormier climate means this is not the time to let up on efforts to keep nutrients out of Lake Erie.
“I think we just need to double down on the efforts that we already know are working,” she said.
Emery pointed to wetlands as one of the clearest tools available, both on public wildlife areas and on private farmland, for stripping nutrients out of water before it reaches Lake Erie.
She also mentioned less common practices in Ohio, such as two‑stage ditches, that have shown promise in Indiana. Ohio State University describes them as “ditches within a ditch” that add a wide, vegetated shelf (called a bench) alongside the main channel. During heavy rains, that bench floods, slowing the water so sediment and attached nutrients can settle out instead of racing downstream. Research has shown it can cut dissolved algae‑ready phosphorus and reduce muddy runoff. Separately, Ohio State is now testing a potentially game-changing in‑lake treatment that could help reduce cyanobacteria and blunt harmful algal blooms once they form that appears to avoid heavily disturbing the rest of the aquatic ecosystem.
“There are lots of institutions that are working really well together to try to both monitor problems in Lake Erie as well as trying to study solutions on the land,” Emery added. “I think the work that NOAA does to pull all the data together and make this forecast every year is really vital, and so we need to keep supporting federal programs like NOAA, because the work that they do with regional institutions is really important.”
