Scientists predict mild harmful algal bloom for Lake Erie this year

Lake Erie

Lake Erie is expected to have a mild harmful algal bloom this year, according to researchers at Ohio Sea Grant’s 2023 virtual forecast for harmful algal blooms in Lake Erie, June 29.

That’s likely due to a dry spring. Lake Erie’s harmful algal blooms are largely caused by nutrient runoff from farmland, specifically phosphorus. Less water, and therefore less nutrients, flowing into the lake will likely mean a milder bloom.

“It was the driest May since 1934, which was the dust bowl era,” said Laura Johnson, director of the National Center for Water Quality Research at Heidelberg University, during the forecast.

This is the fourth consecutive year the National Oceanic and Atmospheric Administration has predicted a milder than average bloom. In 2021 and 2022, however, the bloom wound up being more severe than originally forecasted, leading researchers to believe that July rainfall is more significant than previously thought.


The forecast for 2023 is a 3 on the severity index, with a potential range of 2-4.5. The severity index is a scale of 1-10, and anything over a 5 on the index is considered a more severe bloom. The size of the bloom doesn’t necessarily indicate how toxic it is.

In 2022, NOAA predicted an algal bloom with a severity of 3.5. The bloom in 2022 had a final severity of 6.8, according to a November 2022 release from NOAA.

There was a similar difference between the 2021 forecast — a severity of 3 — and the final bloom severity of that year — a 6.0 on the index.

“The blooms are developing in July,” explained Rick Stumpf, oceanographer with NOAA’s National Centers for Coastal Ocean Science. So if heavier rainfall sends more nutrients into the lake at that time, those nutrients are available to the blooms right when they’re growing.

If July brings some intense storms, the bloom could wind up being less mild this year. Currently, July rainfall is predicted to be slightly above average, Stumpf said.

“If it rains some, don’t be too concerned because it’s so dry that a lot of that has to soak into the ground,” he added. “So there’s a lot of catch-up room.”

Researchers have also noticed the peaks of Lake Erie’s algal blooms are lasting longer. In 2010, for example, the bloom peaked at almost an 8 on the index, but that peak only lasted for 10 days. In 2022, the slightly lower peak went on for 20 to 30 days, Stumpf said. Since the severity index currently considers the amount of time the peak lasts as well as the size of the bloom, those longer peaks are likely affecting the forecasts.

“We’re now trying to adjust the severity index to correct for this shift,” Stumpf said.


The amount of phosphorus going into the water overall should be close to targets based on the Great Lakes Water Quality Agreement, said Johnson, most likely because of the dry weather. The agreement aims to cut the amount of phosphorus going into the lake by 40% by 2025.

Concentrations of phosphorus going into the lake, however, remain higher than the target.


Public and private sector programs continue to work on the issue. The Ohio Agriculture Conservation Initiative announced in May that more than 2,000 farmers in northwest Ohio have gotten involved with its certification program since 2020, when the program launched.

That program helps farmers develop nutrient management plans to improve water quality. It also works with the H2Ohio initiative, Ohio’s water quality improvement plan, to help farmers fund best management practices to improve water quality. While the H2Ohio program currently covers 24 counties in northwest Ohio, the certification program is available statewide.

It takes time to see results, partly because scientists estimate 60-80% of the phosphorus load into Lake Erie is legacy phosphorus, built up in farm fields from years of fertilizer applications. Researchers have been working on ways to identify which legacy phosphorus fields are likely to have a lot of runoff, and to reduce the phosphorus coming from those fields through things like phosphorus filters.

“It’s a tough problem. We’re doing the right things to move in the right direction,” said Christopher Winslow, director of Ohio Sea Grant.


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