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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.

Additional information is provided in the PWS HAB Response Strategy (2022)

Monitoring Schedules

2022-2023 Off-season Monitoring for HABs

With the new 2022 HAB rule, FINISHED water microcystins monitoring is now required during the off-season. Biweekly schedule sampling will maintain the same schedule as the HAB monitoring season throughout the off-season (starting Dec. 4, 2022). The biweekly schedule is posted below.

Routine Monitoring Systems (Previous schedule 1, 2, and 4) are require to sample biweekly for finished water microcystins (no raw water or cyanobacteria screening).

Reduce Monitoring Systems (Previous schedule 3) are required to sample monthly for finished water microcystins (no raw water or cyanobacteria screening). 

If microcystins are detected in finished water greater than 0.3 ug/L (reported value greater than or equal to 0.35 ug/L)

  • PWS must collect one resample of raw and finished water within 24 hours of an action level exceedance and collect an additional repeat sample of raw and finished water within 24 hours of resample. Analysis must be completely within 24 hours in each case.
  • If microcystins are greater than 0.3 ug/L in either resample or repeat, PWS notifiy all consecutive systems within three hours of receiving the results. 
  • PWS will sample raw water once per week and increase sampling to three times per week at the finished water sampling point.
  • PWS can resume routine monitoring when microcystins are non-detect in finished water for two consecutive samples. 

Biweekly Monitoring Schedule for Routine PWS:

Off-season Biweekly Microcystins Dates

12/4/2022 - 12/10/2022

12/18/2022 - 12/24/2022

1/1/2023 - 1/7/2023

1/15/2023 - 1/21/2023

1/29/2023 - 2/4/2023

2/12/2023 - 2/18/2023

2/26/2023 - 3/4/2023

3/12/2023 - 3/18/2023

3/26/2023 - 4/1/2023

4/9/2023 - 4/15/2023

4/23/2023 - 4/29/2023

5/7/2023 - 5/13/2023


START OF HAB SEASON (first full week of June)


IMPORTANT 2022 HAB Rule Update

The Ohio Environmental Protection Agency, Division of Drinking and Ground Waters (DDAGW ) has adopted the amended rules in the Ohio Administrative Code (OAC) Chapter 3745-90 (posted under DDAGW  Proposed Rules until effective date) along with the amended Ohio EPA Method 701.0 - Total (Extracellular and Intracellular) Microcystins - ADDA by ELISA Version 2.4.

The 2022 rule became effective as of  Tuesday, Nov. 1, 2022.

Under the 2022 HAB rule, all surface water systems (excluding consecutive systems) are required to turn in a Treatment Optimization Protocol (TOP) within six months of the effective rule date (due May 1, 2023). Please use the provided Fillable form for HAB Treatment Optimization Protocol and Developing a Harmful Algal Bloom (HAB) Treatment Optimization Protocol- Guidance For Public Water Systems to assist with the TOP creation process. 

Please contact your district HAB coordinator with any questions. To find your district office, please visit the district office webpage.


What is a harmful algal bloom (HAB)?

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.

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.

Responding to & Reporting a Suspected Bloom

All public water system owners/operators are encouraged to read through the "PWS HAB Response Strategy 2022" for guidance on responding to HABs.

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

HAB Response Strategies, Maps, & Data


Maps & Data

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

Laboratory and Analysis

Laboratory Contact List

Laboratories Certified for Cyanotoxin Analysis

Cyanotoxin Information

Analytical Methods for Cyanotoxins 


VIDEO When in doubt, stay out.



General HAB rules 

  • Overview of 2022 HAB Rule Changes


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

Ohio HAB Information

U.S. and World HAB Information


World Health Organization (WHO)

  • World Health Organization home page
  • WHO, 1999. Toxic Cyanobacteria in Water: A Guide to their Public Health Consequences, Monitoring and Management 
  • WHO, 2003. Guidelines for Safe Recreational Water Environments, Vol. 1, Coastal and Fresh Water
  • WHO, 2004. Microcystin LR in Guidelines for Drinking-Water Quality, Chemical
    Fact Sheets.

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


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.


Please contact your district HAB coordinator with any questions. To find your district office, please visit our district office webpage.

Position Name and Email Phone
Section Manager Colin White 614-644-2759
State HAB Specialist Vacant  
HAB Compliance Callie Nauman 614-644-2756
Central District Andy Amornyard 614-369-3817
Northeast District Chris Maslo 330-963-1164
Northwest District Benjamin Sloan 419-419-3718
Southeast District Emily Deshaies 740-380-5253
Southwest District Brian Chitti 937-204-1199