Harmful Algal Blooms (HAB)

Information for Public Water Systems

harmful algal bloom on a lake

Harmful Algal Bloom (HAB) Monitoring

Public water systems with a surface water source(s) must comply with HAB monitoring and reporting rule requirements (OAC 3745-90-03). Public water systems may be eligible for reduced monitoring, based on cyanotoxin occurrence and treatment capability. Please click the links, below, to view the HAB monitoring schedule assignments for each public water system, HAB monitoring requirements by schedule, and HAB sampling triggers and implementation guidance.


2021 HAB Off-season schedules and information will be posted at the end of October.

Additional information is provided in the 2020 HAB Season Webinar and 2020 PWS Response Strategy.


Starting the first week in May, PWSs in Ohio will follow HAB season monitoring requirements per their assigned schedule. All PWS assigned to schedule 1 and 2 are assigned the same biweekly qPCR monitoring periods. PWSs should collect qPCR and microcystin samples based on the assigned HAB season monitoring schedule instructions below.

Schedule 1: PWSs systems must collect weekly raw and finished water microcystins samples and biweekly qPCR samples beginning the week of May 2, 2021. The cyanobacteria screening sample must be paired with the first weekly raw and finished water microcystins samples.

Schedule 2: PWSs will collect their first biweekly qPCR sample the week of May 2, 2021. They will collect their first biweekly raw water microcystins sample the week of May 9, 2021. Cyanobacteria screening and raw water microcystins samples must be collected on alternating weeks thereafter.

Schedule 3: PWSs must collect a monthly qPCR sample beginning May 2, 2021

Schedule 4: PWSs must collect a weekly finished water microcystins sample beginning May 2, 2021.

Biweekly qPCR monitoring requirements for schedule 1 and schedule 2 PWS:

Biweekly qPCR Monitoring
1 Sample Required Between
5/2/2021 and 5/8/2021
5/16/2021 and 5/22/2021
5/30/2021 and 6/5/2021
6/13/2021 and 6/19/2021
6/27/2021 and 7/3/2021
7/11/2021 and 7/17/2021
7/25/2021 and 7/31/2021
8/8/2021 and 8/14/2021
8/22/2021 and 8/28/2021
9/5/2021 and 9/11/2021
9/19/2021 and 9/25/2021
10/3/2021 and 10/9/2021
10/17/2021 and 10/23/2021
10/31/2021 and 11/6/2021

Please contact your district HAB coordinator with any questions. To find your district office, please visit https://epa.ohio.gov/Contact.


Section Manager (Colin White) – (614) 644-2759
Section Supervisor (Emilie Eskridge) – (614) 644-2765
State HAB Specialist (Ruth Briland) – (614) 369-4045
HAB Compliance (Emilie Eskridge) – (614) 644-2765
Central District (Stella Beech) – (614) 728-5332
Northeast District (Chris Maslo) – (330) 963-1164
Northwest District (Ben Sloan) – (419) 419-3718
Southeast District (Jessica Armold) – (740) 380-5236
Southwest District (Brian Chitti) – (937) 204-1199

Cyanobacteria (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.

Prevention and Treatment

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).

Laboratory Information

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

If you see surface scum or something that looks like cyanobacteria at Ohio’s rivers, lakes, or public swimming beaches, report it to Ohio EPA by completing the online bloom report form or the paper form and emailing it to HABmailbox@epa.ohio.gov.

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 Infrastructure Improvements for HABs

Public Water Systems

Community water systems, publicly or privately owned, that operate surface water treatment systems are eligible for the HAB-discounted interest rate under the Water Supply Revolving Loan Account (WSRLA) program. Eligible projects include treatment system components for HAB treatment, interconnections with other public water systems, elevated storage and development of improved source waters. Nominations for design, and/or construction projects that are directly related to addressing issues from harmful algal blooms (HAB) do not have a deadline and can be submitted to Ohio EPA at any time during the program year. 

For more information, please review the instructions for completing the WSRLA HAB nomination form, available on the Division of Environmental and Financial Assistance webpage.

WPCLF Nutrient Reduction Discount

In response to harmful algal blooms (HABs) and their potential effect on water resources and the raw water supply for drinking water systems, Ohio EPA made $100 million available at a 0% interest rate through the Water Pollution Control Loan Fund (WPCLF) in 2015, 2016 and 2017 for equipment to reduce phosphorus and other nutrients. In 2018, Ohio EPA is offering $50 million at a 0% interest rate for these types of projects. The discounted rate will be available for the portion of the project directly attributed to the nutrient reduction. Standard, below-market interest rate loan funds will be offered for the balance of a proposed project. Ohio EPA will accept nutrient reduction discount (NRD) project nominations for planning, design or construction projects throughout the program year. Applicants who nominated projects for NRD funding in 2017, but did not proceed with projects, and subsequently provided updated schedules during the nomination period to Ohio EPA, will be grandfathered into the 2018 program.

For more information, please review the nutrient reduction guidance and addendum, available on the Division of Environmental and Financial Assistance webpage.

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 Research Australia (WaterRA)

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
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