CHICAGO — Nov. 10, 2015 — Scientists from the National Oceanic and Atmospheric Administration’s (NOAA) National Centers for Coastal Ocean Science and Great Lake Environmental Research Laboratory released their analysis of the 2015 algal bloom in western Lake Erie, which showed the bloom was the worst in 100 years.

Scientists use the severity index to measure the amount of biomass in the bloom, noted the bulletin. The index is 10.5 for 2015, compared to 10 for the 2011 bloom.

In contrast to the 2011 bloom which ran along the shore, the 2015 algal bloom moved into the center of the central basin, stated the bulletin. This occurrence helped lessen the bloom’s impact on the central basin coasts.

A July forecast predicted the bloom would be the second worst since measurements began in 2002, with a severity index of 8.7, reported the bulletin. The current bloom began earlier than normal in mid-July and grew to its maximum size in mid-August.

Scientists explained in the bulletin that in a 40-day period from late July to the end of August, they detected the largest biomass they had ever monitored during a time period, except for the first week of October 2011. Scum covered up to 300 square miles on Aug. 5 and Aug. 15.

Cold fronts in September weakened the bloom and disrupted its growth, resulting in a faster decline than observed in other major blooms, shared the bulletin.

Models show that while the forecast correctly predicted an extremely large algal bloom, it was an underestimate, noted the bulletin. When considering nutrient levels and high discharge from heavy rains, a revised forecast would have predicted a bloom at least as large as the one in 2011.

You can find the entire bulletin here.