NOAA and its research partners are forecasting a moderate harmful algal bloom (HAB) in western Lake Erie this summer. This year's bloom is expected to measure 3.5 on the HAB severity index, with a potential range of 3 to 4.5.
Experts from NOAA and their government and academic partners discussed the 2026 Seasonal Forecast of Harmful Algal Blooms for Lake Erie during a free public webinar today hosted by Ohio Sea Grant and Stone Laboratory.
"Toxic algae affect not only the health of people and Great Lakes ecosystems, but they can negatively impact local and regional economies by preventing people from fishing, swimming, boating and visiting the shoreline," said Nicole LeBoeuf, assistant administrator for NOAA's National Ocean Service. "NOAA's Lake Erie harmful algal bloom forecast 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."
The HAB severity index is based on the bloom's biomass (the amount of algae) during the peak 30 days of the bloom. Moderate blooms have an index of 3 to 5, while an index above 5 indicates more severe HABs. Blooms over 7 are particularly severe, with extensive scum formation and persistent bloom coverage affecting the lake.
NOAA expects to see a visible bloom by mid-July. The bloom's timeline will depend on the frequency of high winds in September, which cannot be predicted this far in advance. Most of the bloom will remain in areas of the lake's western basin. The central basin of the lake is usually unaffected until later in the season, although localized blooms may occur around some of the rivers after summer rainstorms.
Lake Erie HABs consisting of cyanobacteria (i.e. blue-green algae) are capable of producing microcystin, a known liver toxin that poses a risk to human and wildlife health. Such blooms can sometimes require cities and local governments to add more treatment to drinking water and close beaches.
The size of a HAB is not necessarily an indication of how toxic it is. Each algal bloom is unique in terms of size, toxicity and ultimately its impact on local communities. NOAA continues to develop new tools to detect and predict how toxic blooms will be.
NOAA will issue a seasonal forecast update in late July based on observed nutrient loads from the Maumee River watershed into the western basin.
NOAA's National Centers for Coastal Ocean Science's (NCCOS) Lake Erie HAB Forecast website provides predictions and visualizations of the bloom's location and movement on the lake's surface, as well as where the bloom is located within the water column. This information is especially helpful to water treatment plant operators because intake structures are usually located below the surface, so the risk of toxins in their source water may be greater when these cells sink.
In addition to the early season projections, NOAA issues HAB forecasts during the bloom season. These forecasts provide the current extent and 5-day outlooks, which include predictions of where the bloom will travel and the concentrations of blue-green algae which are likely to be seen, allowing local authorities to make informed management decisions.
Additionally, NOAA forecasts hypoxia in Lake Erie's central basin.
Nutrient load estimates for the forecasts came from Heidelberg University in Ohio, and the various forecast models are run by NCCOS, the University of Michigan, and North Carolina State University. The field observations used for monitoring and forecasting are collected in partnership with a number of NOAA offices, including its Ohio River Forecast Center, NCCOS, Great Lakes Environmental Research Laboratory and Cooperative Institute for Great Lakes Research, as well as Ohio Sea Grant, The Ohio State University's Stone Laboratory, The University of Toledo, Ohio Environmental Protection Agency and the U.S. Geological Survey.
