Lake Erie Harmful Algal Bloom FAQs

NOAA's Lake Erie Harmful Algal Bloom Forecast System

The official source of forecasts regarding harmful algal blooms of Karenia brevis (commonly known as red tide) in the Gulf of Mexico and of cyanobacteria (most commonly the species Microcystis aeruginosa) in Lake Erie. The routine HAB forecasts help members of the public make informed decisions when a bloom is temporarily affecting their area. The forecasts also aid people responsible for responding to bloom impacts.

View the most recent forecast here or subscribe to receive an email when the forecast is updated by signing up here.

  • Lake Erie Harmful Algal Bloom Early Season Projections are issued weekly starting in mid-May. The blooms of cyanobacteria (also called “blue-green algae”) are driven primarily by the nutrient load from March to July. The early season projections estimate bloom severity based on measurements and forecasts of phosphorus loading in the Maumee River, the main source of nutrients for these blooms. NOAA models for river discharge through July are combined with observations made by Heidelberg University to estimate the phosphorus load into Lake Erie for the loading season (March to July). These early seasonal projections provide a general sense of how “bad” the upcoming bloom season might be.
  • At the end of June, NOAA issues a final seasonal forecast, which combines a more rigorous set of models to estimate the severity of the bloom for the summer.
  • The Lake Erie Harmful Algal Bloom Forecast system is updated nearly daily throughout the bloom season (July - October). Alerts are sent out to subscribers as conditions change or NOAA feels an alert is necessary.  Each forecast provides current bloom location and extent, the estimated area of the bloom, the potential for mixing and scum formation and a forecast of transport and bloom intensity over 120 hours, as well as the predicted winds, currents, and water temperature. View the most recent forecast here or subscribe to receive an email when the forecast is updated by signing up here.
  • At the end of each HAB season, sometime in late October, NOAA provides a seasonal assessment. This is a retrospective analysis of the bloom.  Microcystis blooms essentially stop growing when the water temperature drops below 65°F.  The blooms decline rapidly after that.

The Lake Erie HAB Forecast provides information about the current location of the bloom and predicts its location over the next few days. This helps stakeholders target their response to minimize impacts. Through the use of this information:

  • Water treatment managers can chemically treat the water, or some plants use a temporary alternative source including a second intake or reservoir.
  • State agencies can guide toxin sampling efforts and close beaches where toxins exceed recreational swimming standards as well as issue warnings for pets.
  • Commercial and recreational boaters can plan activities that are outside of the bloom.


Lake Erie HAB bulletins are issued beginning on the first Monday in July and cease when the Microcystis bloom dissipates. Microcystis blooms require a minimum water temperature of 65°F and so the typical bloom season extends from July to October.
During an active bloom, bulletins are released on Monday and Thursday. Since the bulletin relies on clear satellite imagery to produce accurate forecasts, the bulletin may be delayed by up to one day following overcast weather to allow for better imagery. Bulletins will also be delayed by up to one day following federal holidays.

A complete description of the bulletins is provided in the Lake Erie HAB Forecast Guide. The following products are included:

  • Satellite Imagery: Most recent satellite imagery from the Ocean Land Color Imager (OLCI) and true color imagery showing the bloom location and extent.
  • Bloom Position Forecast: Potential bloom position is forecast based on satellite imagery that *is *used to initiate the model. Modeled surface currents are produced by a 3-dimensional circulation model, and used to move the bloom around and forecast its position over the next 96 hours (Rowe et al., 2016).
  • Mixing forecast: Vertical mixing of cyanobacterial cells through the water column reduces the visibility of the bloom at the surface. Forecasts of mixing and surface scum formation for a minimum of 96 hrs are based on mixing in the 3-dimension model, using predicted winds as input.

Forecast resources routinely included:

  • Ocean color satellite imagery derived from Copernicus Sentinel-3 satellite data from the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT) and processed by NOAA, National Centers for Coastal Ocean Science
  • Surface wind and currents observations from the Lake Erie Operational Forecast System (LEOFS).
  • Water sample analysis from the Great Lakes Environmental Research Laboratory (GLERL).
  • Microcystis and toxin sampling from state agencies and academic institutions.
  • National Weather Service (NWS) water temperature observations and forecasts.
  • Buoy wind data from NOAA's National Data Buoy Center

See our Contributors & Data Providers page for more detail.

The intensity and the extent of the area impacted by the bloom varies significantly from year to year. Before a bloom develops in Lake Erie, NOAA researchers, with their partners at Heidelberg University, provide experimental early season projections of the severity of the bloom for that bloom season. For the location of the bloom, Lake Erie HAB forecasts provide predictions no more than three to four days in advance because it is not possible to reliably forecast bloom transport, mixing, or potential decline further into the future due to the variation of the environmental conditions the forecasts are based on. Forecasts are updated daily.

About Cyanobacteria and Harmful Algal Blooms

Algae is the term for simple plants that range from microscopic, single-celled organisms to large seaweeds. Harmful algal blooms are the rapid growth of microscopic algae that can negatively impact human and animal health. Read more from NOAA here.

Cyanobacteria (also known as blue-green algae) are bacteria that can photosynthesize (use sunlight to create food) like plants. Although they are single-celled, they can form large colonies that are visible to the naked eye. Some species of cyanobacteria can produce toxins, like the most common bloom forming genus in Lake Erie, Microcystis. Read more about cyanobacteria from NOAA's National Ocean Service here and the EPA here.

To learn more about why harmful algal blooms occur and the research that is being done, visit the National Ocean Service Ocean Facts here. To read about the research being done to understand harmful algal blooms in Lake Erie, visit the Great Lakes Environmental Research Laboratory (GLERL) research page.

Harmful Algae/Cyanobacteria Impacts & Health Questions

The most common bloom forming genus of cyanobacteria, Microcystis can form a layer of green scum in Lake Erie and it produces a toxin called microcystin. Scums form after a period of calm winds, which allows buoyant Microcystis cells to accumulate at the surface. In bloom-level concentrations, the scums can clog the coolant systems of boat engines, and may lead to closures of some beaches. The toxin, microcystin, can pose a risk to drinking water, cause skin irritation, and negatively affect wildlife, pets, and livestock. Health officials conduct routine monitoring to ensure that public drinking water is safe. People should use caution when engaging in activities in or on the water during a Microcystis bloom. For information regarding exposure to Microcystis and symptoms of microcystin, visit the Ohio Department of Health's HAB page. To seek medical advice concerning Microcystis, contact your health provider or find your local health department in Ohio or Michigan.

  • You can still boat and recreate in Lake Erie waters, but be aware that HABs may be present.
  • What you can do:
    • If you can, plan your trip by checking NOAA's HAB forecast before you go.
    • Respect any waterbody closures announced by local public health authorities.
    • Avoid in-water activities in areas where the water is discolored by algae or scums are visible.
    • Thoroughly wash yourself and pets after suspected contact with a HAB.
  • Find out more information:

Commercial fish from local restaurants and markets is safe to eat. If you catch fish:

Additional Information Concerning Harmful Algal Blooms in Lake Erie

  • Wynne, T.T., Stumpf, R.P., Briggs, T.O. 2013. "Comparing MODIS and MERIS Spectral Shapes For Cyanobacterial Bloom Detection." International Journal of Remote Sensing.
  • Wynne, T.T., Stumpf, R.P. 2015. "Spatial and Temporal Patterns in the Seasonal Distribution of Toxic Cyanobacteria in Western Lake Erie from 2002-2014." Toxins. Volume 7. Pages 1649-1663.
  • Wynne, T. T., Stumpf, R. P., Tomlinson, M. C., Warner, R. A., Tester, P. A., Dyble, J. and Fahnenstiel, G. L. (2008) “Relating spectral shape to cyanobacterial blooms in the Laurentian Great Lakes”, International Journal of Remote Sensing, 29:12, 3665 — 3672
  • Wynne, T.T., Stumpf, R. P., Tomlinson, M. C., Schwab, D. J., Watabayashi, G. Y., Christensen, J. D. 2011. “Estimating Cyanobacterial Bloom Transport by Coupling Remotely Sensed Imagery and a Hydrodynamic Model.” Ecological Applications. Vol 21, 7, pp. 2709-2721.
  • Wynne, T.T., Stumpf, R. P., Tomlinson, M. C., Dyble, J. 2010. “Characterizing a Cyanobacterial Bloom in Western Lake Erie Using Satellite Imagery and Meteorological Data.” Limnological Oceanography. Vol. 55, 5, pp. 2025-2036.
  • Wynne, T.T., Stumpf, R. P., Tomlinson, M. C., Fahnenstiel, G. L., Dyble, J., Schwab, D. J., Joshi, S. J. 2013. “Evolution of a Cyanobacterial Bloom Forecast System in Western Lake Erie: Development and Initial Evaluation.” Journal of Great Lakes Research. Vol 39, pp. 90-99
  • Stumpf RP, Wynne TT, Baker DB, Fahnenstiel GL (2012) Interannual Variability of Cyanobacterial Blooms in Lake Erie. PLoS ONE 7(8): e42444. doi:10.1371/journal.pone.0042444