Western Lake Erie: bloom size is not toxicity

In spring the Maumee River carries phosphorus into the shallowest corner of Lake Erie, and by summer the basin turns. NOAA forecast this year's at 3.5 on a scale where 3 to 5 is moderate, which is a sentence about how much algae there will be and not about how toxic it is.

The western basin is where the Maumee arrives, and the phosphorus arrives with it. EPA's nutrients annex sets a 40 percent reduction in spring total and soluble reactive phosphorus loads from that river, calculated against 2008 because 2008 looked like an average year, and a 40 percent cut in total phosphorus to the western and central basins to bring the central basin to 6,000 metric tons a year. Those targets were adopted in February 2016.

Worth knowing what the forecast number is made of. The index NOAA forecasts is built from the bloom's biomass over its peak thirty days, which is a measure of how much algae there is rather than of how toxic it is. Both matter to a utility, and they are not the same reading.

Nicole LeBoeuf, who runs NOAA's National Ocean Service, put the purpose of the forecast plainly: it is designed to provide timely, science-based information to water managers and public health officials as they make decisions to protect their communities and visitors.

NOAA's seasonal forecast, 25 June 2026: https://coastalscience.noaa.gov/news/moderate-harmful-algal-bloom-predicted-for-western-lake-erie-in-summer-2026/ EPA on the nutrients annex, last updated 18 March 2026: https://epa.gov/glwqa/about-nutrients-annex-annex-4