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A "significant harmful" algal bloom is being forecast for western Lake Erie this summer as researchers seek ways to deal with the outbreak, the National Oceanic and Atmospheric Administration reported Thursday.

Scientists from the University of Michigan said this year's bloom could measure 7.5 on the severity index, but could range between 6 and 9 with an index above 5 indicating a greater impact. The federal NOAA funds UM's research.

The severity index is based on the amount of algae over a sustained time period.

The algal bloom, researchers said, is not expected to take off until late July because the lake temperature has been cooler due to increased rainfall in the area. Later this month, water temperatures are expected to reach 65 to 70 degrees Fahrenheit.

"Because of the excessive spring precipitation, this year’s bloom is likely to be large," said University of Michigan aquatic ecologist Don Scavia, a member of the forecast team. "But bloom predictions — regardless of size — do not necessarily correlate with public health risk. Local weather conditions such as precipitation, wind direction and water temperature also play a role."

The presence of large algal blooms in Lake Erie's western half has become an annual occurrence. The green slime that fouls local beaches is generated, in part, by nutrients like phosphorus that make their way into the watershed.

While there are multiple sources of phosphorus, large farming operations are often cited as a major contributor to the problem.

Researchers said that the largest blooms happened last in 2010 with a severity index at 10 and 10.5 in 2015.

But it was in August 2014, with a lower forecast severity index, that local government officials issued a three-day advisory on drinking water after testing showed traces of toxic algae. As a result, 400,000 Ohio residents were without water, as well as 30,000 in Michigan's Monroe area.

Last year, the index was at 3.6 while in 2017 it spiked to 8, officials said.

More tranquil winds in the summer tend to allow the algal toxins to concentrate, making blooms more harmful, researchers said. The bloom typically peaks in the western part of the lake in September.

Most of the rest of the lake will not be affected.

"This extremely wet spring has shed light on the movement of nutrients from the land into Lake Erie," said Christopher Winslow, director of Ohio Sea Grant and Stone Laboratory. "Despite the predicted size of this year’s bloom, portions of the lake will be algae-free during the bloom season and the lake will remain a key asset for the state."

Continued research helps "us understand bloom movement and toxin production, and remains vital to providing our water treatment facilities with the tools, technology and training they need to keep our drinking water safe," Winslow said.

lfleming@detroitnews.com

(313) 222-2620

Twitter:@leonardnfleming

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