Harmful Algal Blooms (HAB)

Information for Public Water Systems

harmful algal bloom on a lake

Prepare Now for Reduced Harmful Algal Bloom (HAB) Off-Season Monitoring (November 4, 2018 – May 4, 2019)

Starting November 4, water systems that have not detected microcystins or mcyE genes in their source water for at least two consecutive weeks are eligible for reduced off-season HAB monitoring. View the guidance document for details.

Please note, the monitoring schedules presented below remain in effect until further monitoring reductions become available for eligible water systems on November 4. Ohio EPA will update this website with off-season monitoring schedule information the week prior to the new schedules going into effect.


State HAB Coordinator (Heather Raymond) – (614) 644-2911
State HAB Specialist (Ruth Briland) – (614) 369-4045
Central District (Tya Darden) – (614) 728-3866
Northeast District (Chris Maslo) – (330) 963-1164
Northwest District (Ben Sloan) – (419) 419-3718
Southeast District (Jessica Dingman) – (740) 380-5236
Southwest District (Brian Chitti) – (937) 204-1199


HAB Off-Season Monitoring Requirements for Ohio Public Water Systems

Starting November 4, 2018, PWSs that have not detected microcystins in raw or finished water samples for at least two consecutive weeks are eligible for reduced HAB monitoring. Eligible water systems may elect to follow the off-season schedule specified in rule, biweekly raw water microcytins AND paired biweekly raw water qPCR screening, or follow further reduced monitoring schedules specified below:

Monitoring Schedule 2018 HAB Off-Season Monitoring Requirements
(11/4/18 - 5/4/19)
1 and 2 Reduced HAB Season Schedule 1/2
  • Biweekly raw water microcystins; OR
  • Biweekly qPCR screening 
3 Reduced HAB Season Schedule 3
  • Monthly raw water microcystins; OR
  • Monthly qPCR screening


  • Ohio EPA will assume all eligible PWSs will elect to conduct microcystins only off-season monitoring unless they indicated their preference for qPCR screening to Ohio EPA in writing.
  • PWSs may not change between microcystins and qPCR monitoring during the off-season.
  • During the off-season, if mcyE genes or microcystins are detected in the raw water:
    • PWS must collect paired raw and finished water microcystins samples within 24 hours of receiving the result and complete analysis within five days. If PWS already collected a finished water microcystin sample with a raw water microcystins sample, an additional raw and finished water sample is not required until the following week.
    • PWS will continue with weekly paired raw and finished water microcystins monitoring until non-detect for at least two consecutive weeks, then PWS is eligible to transition to off-season monitoring Schedule 1/2.
  • Raw water microcystins detections >5ug/L and finished water microcystins detection trigger additional monitoring requirements (see OAC Rule 3745-90-03).
  • Schedule 1 and 2 water systems that are eligible for reduced off-season raw water monitoring that elect to conduct qPCR screening must continue to collect qPCR samples on the same week they currently conduct qPCR screening. Eligible water systems that elect to conduct microcystins only monitoring in the off-season must sample for microcystins on the alternate week.
  • Consecutive systems that purchase water from out of state systems are not eligible for additional on-season or off-season reduced monitoring, they will continue following OAC Rule 3745-90-03.
  • Any PWS has the option to follow monitoring according to OAC Rule 3745-90-03.

More information can be found by viewing the guidance document located at the top of the page. Please contact your district HAB coordinator with any questions.

NOTE: It is the responsibility of the PWS to identify their eligibility for reduced monitoring and recognize that off-season microcystins or mcyE gene detections trigger follow-up paired raw and finished water microcystins monitoring.

**Wellston South Plant is eligible for Schedule 3
**Out-of-State purchased water plant, required to collect a minimum of one finished water sample biweekly analyzed for total microcystins beginning the week of Oct. 29, 2017 per (OAC 3745-90-03)

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

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 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 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

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.