TRAVERSE CITY, MI -  A "significant" harmful algae bloom is likely to form in western Lake Erie this summer, though it probably won't be as large as some previous formations that posed health risks and hampered tourism, scientists said Thursday.

The National Oceanic and Atmospheric Administration and research partners released their annual algae forecast for the shallowest and warmest of the Great Lakes, where massive algae formations are a recurring threat to the environment and the economy. Toxic contamination from a 2014 bloom prompted a two-day shutdown of tap water systems for 400,000 people in Toledo, Ohio, and southeastern Michigan.

Researchers have developed a scale for rating the severity of a bloom based on how much algae it contains over a sustained period. They predict this year's will register a score of seven, though it could range anywhere from six to eight.

A rating above five indicates a potentially harmful level, meaning such blooms could do damage by generating toxins or sucking enough oxygen from the water to cause fish kills.

When they developed the scale, researchers thought the maximum score would be a 10. A 2011 bloom reached that mark and a 2015 bloom exceeded it, registering a 10.5 as the biggest bloom on record. It's worth noting that a bloom's size doesn't necessarily reflect its toxicity.

Recent algae formations in western Lake Erie have taken shape in late July and grown bigger in early August. A similar pattern is expected this year, scientists said.

"A bloom of this size is evidence that the research and outreach efforts currently underway to reduce nutrient loading, optimize water treatment, and understand bloom dynamics need to continue," said Christopher Winslow, Ph.D., director of the Ohio Sea Grant College Program.

But he added that despite its anticipated size, "much of the lake will be algae-free throughout the bloom season and the lake remains a key asset."


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