Lake Erie’s harmful algal bloom smaller than expected, half as bad as 2019

2020 harmful algal bloom

The Microcystis cyanobacteria bloom biomass in western Lake Erie at the peaks in Aug 1-10, 2019 (left) and Aug 21-31, 2020 (right), showing the difference in intensity. Blue color indicates low concentrations that would not be immediately obvious to the eye. Areas that are red had greater likelihood for scum formation. While 2020 had a larger area of cyanobacteria, most of this was low concentration with low risk for toxins. In contrast, the 2019 bloom had a much larger area of high concentration.

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CLEVELAND, Ohio -- Lake Erie’s annual harmful algal bloom was less severe than expected, rating a 3 on a scale of 1-10.

The National Oceanic and Atmospheric Administration had forecasted a rating of 4.5. Last year, the bloom was a 7.3, after a forecast of 7.5.

The bloom started in late July and reached a peak during the last week of August, according to NOAA. It weakened quickly in September, after several days of strong winds.

The blue-green toxic algae is an annual problem in Lake Erie, from Toledo to the islands. The algae turns fresh water into pea soup, with thick mats of scum that can close beaches, wreck tourist fishing and contaminate drinking water, as it did in Toledo in 2014. The worst blooms in the last decade have been 2011 and 2015.

The size of the annual spread depends on how much rain falls on Northeast Indiana, Southeast Michigan and Northwest Ohio between March and July, how heavy the rain is and how much phosphorus runs off farms into the Maumee River, and then Lake Erie. Warm weather and less wind makes the bloom bigger, though not necessarily more toxic.

Scientists forecast the severity of the harmful algal bloom each spring, using a combination of different models. One model correctly forecast the severity, while others over-estimated, NOAA said. Scientists will examine the differences in forecasts from previous years to evaluate the models.

With cool lake temperatures in May and early June, the cyanobacteria -- harmful blue-green algae -- only started growing in early July, NOAA said. There was less rain than average in the Maumee watershed.

Gov. Mike DeWine introduced the $172 H2Ohio plan to pay farmers who follow a 10-step phosphorus reduction program – which includes steps that crop rotation, slowing water runoff, and minimize the impact of the fertilizers and manure that contain the phosphorous – to keep the chemical out of the lake.

Nearly 2,000 farmers submitted applications to enroll more than 1.1 million acres of land.

2020 harmful algal bloom

Lake Erie's harmful algal bloom in 2020 is expected to be moderate, based partly on a drier spring.

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