Harmful Algal Blooms (HAB)

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.

Begin Preparations for 2017 Harmful Algal Bloom (HAB) Season

Ohio EPA offered outreach in the Spring of 2017 to Public Water Systems (PWSs) outlining key-changes for the 2017 HAB season. The information was captured in a webinar. A recording and slides can be viewed below.

WEBINAR: 2017 HAB Season Update for Ohio PWS

Questions? Contact your Ohio EPA District HAB coordinator:
Central District (Tya Darden) – (614) 728-3866
Northeast District (Chris Maslo) – (330) 963-1164
Northwest District (Kimberly Burnham) – (419) 373-3102
Southeast District (Lesley Jenkins) – (740) 380-5236
Southwest District (Brian Chitti) – (937) 204-1199

Reduced Monitoring Requirements for Ohio Public Water Systems (**COMING SOON**)

HAB Maps and Strategy

Public Water System HAB Response Strategy

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. 

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 an Algal Bloom

Individuals reporting algal blooms 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

Lab Techniques for Detecting Microcystins in Water Using Enzyme-Linked Immunsorbent Assay (ELISA)
This video demonstrates how to measure a particular group of toxins following the Ohio EPA Total Microcystin Analytical Methodology using an ADDA-ELISA kit.


 VIDEO  When in doubt, stay out.

Funding Opportunities for Cyanotoxin Testing Equipment and Infrastructure Improvements

Cyanotoxin Grant Application Extended and Amount Increased: The June 1, 2015, deadline has been removed for submitting grant applications for cyanotoxin testing equipment and training. Applications will be accepted as long as funds are available.​ Also, the maximum amount granted to each public water system has now increased to $30,000 (from $20,000).

  • Grant Application and Guidelines for Cyanotoxin Testing Equipment 
    Ohio EPA has increased the amount of grant funds available for cyantoxin testing equipment for each public water system using surface water to $30,000. These funds may be used for the purchase of equipment, supplies and training for analysis of toxins associated with HABs, such as:
  • Grant Opportunity for Cyanotoxin Testing Equipment for Water Systems Webinar
    • Questions and Answers from Aug. 15, 2014 (Word) (PDF)
    • Questions and Answers from Aug. 22, 2014  (Word) (PDF)

Guidance for Conducting Enzyme-linked Immunosorbent Assay (ELISA) Testing for Microcystin

For more information on funding incentives, click here.

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)

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

Ohio EPA Introduces New Harmful Algal Bloom Advisory System
A new multi-tiered advisory system to notify the public if microcystin, and other compounds produced by blue-green algae, is detected in treated drinking water at local public water systems throughout the state.

Prevention and Treatment

Learn more about types of treatment to address HABs: