Harmful Algal Blooms Info for Public Water Systems

Harmful Algal Bloom (HAB) Monitoring

Public water systems with a surface water source(s) must comply with the updated HAB monitoring and reporting rule requirements (OAC 3745-90-03). HAB Season monitoring will being the first full week of June (starting June 1, 2025) and continue to the first full week of December. Please use the information provided blow to view the HAB monitoring schedule assignments for each public water system. Additional information on HAB sampling triggers and implementation guidance can be found in the documents linked below.

• HAB Monitoring Schedule Assignments 
• Monitoring Sampling Triggers and Implementation Notes 

More detailed information is provided in the PWS HAB Response Strategy

Monitoring Schedules

2025 HAB Season Monitoring: Microcystins and Cyanobacteria Screening (qPCR) Sampling
Starting the first full week of June (6/1/2025), PWSs in Ohio will follow off-season season monitoring requirements per their assigned schedule. PWSs should collect cyanobacteria screening and microcystins samples based on their assigned HAB Monitoring Schedule Assignments.

Routine Monitoring: PWSs are required to monitor for their first biweekly raw water microcystins sample the week of June 1, 2025. PWSs are required to monitor for their first raw biweekly raw water cyanobacteria screening sample the week of June 8, 2025. Cyanobacteria screening and raw water microcystins monitoring must be occur on alternating weeks thereafter. 

Reduced Monitoring: PWSs are required to monitor for a monthly raw water cyanobacteria screening sample starting June 1, 2025.

PWS purchased out-of-state surface water: PWSs are required to monitor for finished water microcystins once a week. The first sampling week is June 1-7, 2025.

For any system with a raw water detection please follow the guidelines here: Monitoring Sampling Triggers and Implementation Notes 

If microcystins are detected in the finished water greater than 0.3 ug/L:

• PWS must collect one resample of raw and finished water within 24 hours of action level exceedance and collect and additional repeat sample of raw and finished water within 24 hours of the resample. Analysis must be complete within 24 hours in each case.
• If microcystins are greater than 0.3 ug/L in either the resample or repeat (finished water), PWS must notify all consecutive systems within three hours of receiving the results. 
• PWS will monitor 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.

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

Basics

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.

• Attend the Algae Identification Workshop offered by Stone Laboratory during the summer months.
• Bloom Characterization Guide - Photographs of assorted blooms: includes HABs, non-harmful green algae blooms and duckweed

Responding to & Reporting a Suspected Bloom

All public water system owners/operators are encouraged to read through the "PWS HAB Response Strategy" 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. 

VIDEO When in doubt, stay out.

Prevention and Treatment

• AWWA White Paper on Cyanotoxin Treatment (2016)
• Division of Surface Water Permit OH870003 Page
  • General Permit (OHG870003) for Discharge of Pesticides and Algaecides
  • Fact Sheet
• Developing a Harmful Algal Bloom Treatment Optimization Protocol-Guidance for Public Water Systems
• Fillable form for HAB Treatment Optimization Protocol
• Developing a Cyanotoxin General Plan- Guidance For Public Water Systems

HAB Response Strategies, Maps, & Data

Strategies

• Public Water System Harmful Algal Bloom Response Strategy
• Ohio HAB Response for Recreational Waters

Maps & Data

• Public Water System Station IDs
• Ohio Public Water System Lakes
• Public Water System HAB Data and Map
• Ohio EPA Drinking Water Advisories
• Beachguard (Recreational and Beach Monitoring Data and Advisories)

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.

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 and Analysis

2025 Lab Refresher for Harmful Algal Bloom (HAB) Monitoring

Laboratory Contact List

Laboratories Certified for Cyanotoxin Analysis

Cyanotoxin Information

• Environmental Technology Verification (ETV) Reports for microcystin test kits
• List of Toxin Producing Cyanobacteria
  • This list includes some genera of cyanobacteria known to produce toxins

Analytical Methods for Cyanotoxins

• Ohio EPA Method 701.0-Total( Extracellular and Intracellular) Microcystins — ADDA by ELISA Version 2.4 (Effective Nov 2022)
• Ohio EPA DES 705.0, Quantitative Polymerase Chain Reaction (qPCR) for Determination of Cyanobacteria and Cyanotoxin-Producing Genes Analytical Methodology

Rules

General HAB rules

• 2022 HAB Rules

Resources

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

Ohio HAB Information

• HAB Be Aware Brochure
• HABs in Ohio Waters Brochure
• HABs in Ohio Waters Poster
• Algae in Ponds Fact Sheet (Ohio Department of Health)
• Cyanobacteria Fact Sheet (Ohio Department of Health)
• Public Water System Harmful Algal Bloom Response Strategy (2022)
• Ohio HAB Response Strategy for Recreational Waters
• Ohio Algae Information for Recreational Waters
• Beachguard Recreational and Beach Monitoring Data
• Ohio Department of Health

U.S. and World HAB Information

U.S. EPA

• Recommendations for Public Water Systems to Manage Cyanotoxins in Drinking Water
• Drinking Water Standards and Regulatory Support for Microbiological Contaminants
• Cyanobacteria Harmful Algal Blooms (CyanoHABS) in Water Bodies
• Harmful Algal Blooms and Drinking Water Treatment
• Water Treatment Optimization for Cyanotoxins (reference Appendix A)

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

• U.S. Geological Survey Kansas Algal Toxins Research Team
• Graham, J, Loftin, K., Meyer, M., Ziegler, A., 2010. Cyanotoxin Mixtures and Taste-and-Odor Compounds in Cyanobacterial Blooms from the Midwestern United States, Environmental Science and Technology
• Graham, J., Loftin, K., Ziegler, A., and Meyer, M., 2008. Guidelines for design and sampling for cyanobacterial toxin and taste-and-odor studies in lakes and reservoirs, U.S. Geological Survey Scientific Investigations Report 2008-5038

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

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.

Contacts

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