Experts Predict Smaller Lake Erie Algal Bloom This Summer

Satellite photo of Lake Erie algal bloom

PUT-IN-BAY, Ohio — Experts are predicting that Lake Erie’s harmful algal bloom this summer will be smaller than last year’s, which was the third-largest ever recorded. But the bloom will be larger than the mild bloom in 2016.

The bloom is expected to measure 6 on the severity index, but could range between 5 and 7.5, according to a forecast issued today (July 12) by scientists including from the National Oceanic and Atmospheric Administration (NOAA) and The Ohio State University’s Ohio Sea Grant program.

“Research efforts across the state have helped our communities prepare for blooms of this size, from developing new technologies to keep toxins out of our drinking water to assessing the human health impacts of harmful algal bloom toxins,” Ohio Sea Grant Director Chris Winslow said.

“While continued efforts are still needed to reduce nutrient runoff and therefore the size of future harmful algal blooms, Lake Erie residents and visitors will still be able to safely enjoy much of the lake during bloom season,” he said.

The severity index is based on a bloom’s biomass — the amount of its harmful algae — over a sustained period. Lake Erie’s largest blooms, in 2011 and 2015, were 10 and 10.5, respectively. Last year’s bloom had a severity of 8.

Lake Erie’s harmful algal blooms, concentrated in its western basin, can turn the water green, can hurt tourism businesses and recreation, and can sometimes produce toxins that pose health risks to people, especially if they get into drinking water. Excessive phosphorus, a nutrient present in fertilizers and manure that can be washed from farm fields by rain, is a major cause of the blooms.

The scientists announced the forecast at Ohio State’s Stone Laboratory, of which Winslow is also the director. The lab, part of the College of Food, Agricultural, and Environmental Sciences (CFAES), is located at Put-in-Bay on Lake Erie.

Get forecast updates

NOAA’s forecast was based on factors including spring rain and phosphorus runoff within the lake’s watershed, water temperatures in the lake, and rainfall expected through the rest of the summer and fall.

Twice-weekly updates to the forecast are available at

W. Russell Callender, assistant administrator for NOAA’s National Ocean Service, said NOAA “continues to develop tools that provide early warning systems for harmful algal blooms which help visitors and the community make better informed decisions about recreation activities.”

He said Lake Erie is a driver of northern Ohio’s economy, and “we’ll keep working with our partners to bring the most accurate forecasts for the region.”

Editor: Much of the information in this press release came from a joint NOAA-Ohio Sea Grant press release published on July 12.

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Chris Winslow