Harmful Algal Blooms

Information for Public Water Systems

harmful algal bloom on a lakeCyanobacteria (also known as blue-green algae) are microscopic organisms found naturally in surface water that can sometimes multiply to form harmful algal blooms (HABs).  HABs can potentially produce toxins capable of causing illness or irritation -- sometimes even death -- in pets, livestock, and humans.  In addition to producing toxins, cyanobacteria can pose other treatment challenges for public water systems including taste and odor and shortened filter run times. The information below is provided to assist public water system operators with preventing, identifying, and responding to HABs.

HAB Data and Advisories

  • Map of current advisories
    • Check if any advisories have been posted at public water supplies, Lake Erie, and Ohio State Park beaches
  • Algal toxin results (2011 to present) (Excel) (PDF)
    • Cyanotoxin results across Ohio for public water supplies, Lake Erie, and Ohio State Park beaches

Public Water System HAB Response Strategy and Summary

 VIDEO  When in doubt, stay out.

Visual Bloom Severity and Toxin Concentrations

Visual bloom severity is often not the best indication of toxin concentrations at intake depths.  When the blooms are concentrated at the surface, toxin concentrations at the intake can be lower.  For example, when Lake Erie was covered by extensive surface scums (Figure 1) in 2011, toxins were not detected at the Lake Erie public water system intakes.  So far in 2013, no scums have been reported on Grand Lake St. Marys, but microcystin concentrations at the intake have been much higher (e.g., up to 102.8 ug/L).  

When blooms are more dispersed throughout the water column, and not concentrated in surface scums, intake toxin levels can be higher.  For example, when the picture in Figure 2 was taken at Maumee Bay State Park in 2011, the cyanobacteria were dispersed throughout the water column which resulted in a bloom that did not appear severe visually.  However, the microcystin concentrations at the public water system intake exceeded 5.0 ug/L.  It should be noted that the toxin concentrations at the beach were also high, with microcystin levels exceeding 100 ug/L.  

Lake Erie harmful algal bloom

Maumee Bay State Park harmful algal bloom

Figure 1. HAB at Lake Erie with no toxins detected at the intakes (2011).
Figure 2. HAB at Maumee Bay State Park with a toxin concentration of greater than 5.0 ug/L at the intake (2011).










Responding to a Suspected Bloom Harsha Lake phytoplankton sample

All public water system owners/operators are encouraged to read through the "Public Water System Harmful Algal Bloom (HAB) Response Strategy" for guidance on responding to HABs.

Anyone can report a HAB

Individuals reporting HABs are encouraged to fill out the HAB Report Form and email it, with attached digital photographs if available, to Ohio EPA's HAB Mailbox.

Prevention and Treatment

How to Recognize HABs

Use the following reference documents and photographs to learn more about recognizing HABs.  For additional photographs and information, please visit Ohioalgaeinfo.com.

Analyze Samples for Cyanotoxins

Resources harmful algal bloom on Kelleys Island

To learn more about HABs, check out the list of key references below or visit ohioalgaeinfo.com.

World Health Organization (WHO)

Water Quality Research Australia (WQRA)

2008 International Symposium on Cyanobacterial Harmful Algal Blooms (ISOC-HAB)

U.S. Geological Survey

Water Research Foundation

  • Water Research Foundation home page
  • Algae: Source to Treatment (M57), 2010
  • Removal of Algal Toxins From Drinking Water Using Ozone and GAC, 2002
  • Reservoir Management Strategies for Control and Degradation of Algal Toxins, 2009
  • Early Warning and Management of Surface Water Taste & Odor Events, AwwaRF 2006
  • Identification of Algae in Water Supplies (CD-ROM), AWWA 2001

HAB Brochures and Posters

HAB Fact Sheets

Prevention and Treatment

Learn more about types of treatment to address HABs: