Scientists are warning another massive harmful algae bloom will blanket western Lake Erie this summer.

The algae bloom is forecast to reach a severity of 7.5 on a Harmful Algal Bloom scale of 10, making this a top 5 harmful bloom number in the past 17 years. This falls below the 2011 and 2015 bloom, and is around the bloom severity of 2013 and 2017. 

An index above 5 indicates a potentially harmful bloom. 

2019 Harmful Algae Bloom forecast
NOAA

Scientists with the National Oceanic and Atmospheric Administration released the forecast on Thursday.

Researchers say that record-setting rains in Ohio and neighboring states in recent months will fuel a large mass of algae on the lake.

Algae blooms have become a recurring problem on the shallowest of the Great Lakes, and it was nearly five years ago when a bloom contaminated drinking water here in Toledo in 2014. That toxic bloom caused a two-day shutdown of Toledo's drinking water. 

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Some areas along the Ohio shoreline already have been seeing algae starting to form and drift into the lake.

Heavy rains are to blame for washing farm fertilizer and untreated sewage into the lake.

The Associated Press contributed to this report.