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Water Quality Standards Program

Our water quality is constantly threatened by many different sources and types of pollution. Under the Clean Water Act, every state must adopt water quality standards to protect, maintain and improve the quality of the nation's surface waters. These standards represent a level of water quality that will support the goal of "swimmable/fishable" waters. Water quality standards are ambient standards as opposed to discharge-type standards. These ambient standards, through a process of back calculation procedures known as total maximum daily loads or wasteload allocations form the basis of water quality based permit limitations that regulate the discharge of pollutants into surface waters under the National Pollutant Discharge Elimination System (NPDES) permit program.

U.S. EPA's water quality standards website is at https://www.epa.gov/wqs-tech.


Ohio's water quality standards, set forth in Chapter 3745-1 of the Ohio Administrative Code (OAC), include four major components:

  • beneficial use designations,
  • narrative "free froms",
  • numeric criteria, and
  • antidegradation provisions.

Brief summaries of these components are below.  For a more detailed summary, see:

Implementation of Ohio's water quality standards set forth in Chapter 3745-2 of the Ohio Administrative Code (OAC), includes rules for developing water quality based effluent limitations in NPDES permits for point sources and total maximum daily loads (TMDLs) for discharges of any pollutant requiring control, including toxic, carcinogenic, and organoleptic pollutants.

Beneficial Use Designations

How can I find the use designations for my specific water body of interest?
Go to rules 3745-1-08 to 3745-1-32 of the OAC found within Effective Rules. Each of those rules covers a major drainage basin. Use the Water Body Use Designation Index on that page to find the rule number and page number of your water body of interest.

Ohio drainage basins and associated rule numbers in OAC 3745-1

Beneficial use designations describe existing or potential uses of water bodies. They take into consideration the use and value of water for public water supplies, protection and propagation of aquatic life, recreation in and on the water, agricultural, industrial and other purposes. Ohio EPA assigns beneficial use designations to water bodies in the state. There may be more than one use designation assigned to a water body. Examples of beneficial use designations include: public water supply, primary contact recreation, and aquatic life uses (warmwater habitat, exceptional warmwater habitat, etc.).

Use designations are defined in paragraph (B) of rule 3745-1-07  of the OAC and are assigned in rules 3745-1-08 to 3745-1-32 of the OAC found within Effective Rules. Attainment of use designations is based on specific numeric and narrative criteria. To ensure protection of those beneficial uses, Ohio EPA determines and assigns maximum concentrations for over 100 chemicals.

Narrative "Free Forms"

Narrative "free froms", located in rule 3745-1-04 of the OAC, are general water quality criteria that apply to all surface waters. These criteria state that all waters shall be free from sludge, floating debris, oil and scum, color and odor producing materials, substances that are harmful to human, animal or aquatic life, and nutrients in concentrations that may cause algal blooms.

Much of Ohio EPA's present strategy regarding water quality based permitting is based upon the narrative free from, "no toxics in toxic amounts." Ohio EPA developed its strategy based on an evaluation of the potential for significant toxic impacts within the receiving waters. Very important components of this evaluation are the biological survey program and the biological criteria used to judge aquatic life use attainment.

Numeric Criteria

Numeric criteria are estimations of concentrations of chemicals and degree of aquatic life toxicity allowable in a water body without adversely impacting its beneficial uses. Although numeric criteria are applied to water bodies, they primarily are used to regulate dischargers through NPDES permits.

Numeric criteria consist of chemical criteria, whole effluent toxicity levels and biological criteria.

Chemical Criteria

Aquatic life and human health water quality criteria for individual chemicals are derived from laboratory studies of biological organisms' sensitivity to specific chemicals or combinations of chemicals. In these studies, organisms are exposed to known concentrations of a chemical under varying conditions. For aquatic life water quality criteria, the organisms exposed are a variety of fish, benthic macroinvertebrates and zooplankton. For human health water quality criteria, the organisms exposed are mammals, usually mice or rats.

Based on these tests, guidelines or national criteria recommendations are established by U.S. EPA. Ohio EPA uses these national criteria recommendations in combination with the latest scientific information in setting the appropriate chemical water quality criteria for Ohio's surface waters. Summary tables of aquatic life and human health water quality criteria are available on the Water Quality Criteria & Values tab.

Another class of chemical criteria are those associated with the Agricultural Water Supply use designation. These criteria protect against long term adverse effects on crops and livestock as a result of crop irrigation and livestock watering.

Chemical water quality criteria are in Chapter 3745-1 of the OAC.

Whole Effluent Toxicity Levels

Whole Effluent Toxicity (WET) measures the harmful effects of an effluent on living organisms. A bioassay or toxicity test measures the degree of response of an exposed test organism to a specific chemical or effluent. WET can only be measured using living organisms, not by an instrument. WET consists of acute and chronic toxicity tests. Acute toxicity tests measure the responses of organisms that occur soon after exposure to a test substance. Chronic tests measure the long-term response to test substances. WET measures the accumulative effects of chemicals present in an effluent that cannot be assessed using chemical-specific criteria.

Provisions addressing whole effluent toxicity are in rule 3745-1-44, rule 3745-2-09, and paragraph (B) of rule 3745-33-07 of the OAC.

Biological Criteria

Biological criteria are based on aquatic community characteristics that are measured both structurally and functionally. These criteria are used to evaluate the attainment of aquatic life uses. The data collected in these assessments are used to characterize aquatic life impairment and to help diagnose the cause of this impairment.

The principal biological evaluation tools used by Ohio EPA are the Index of Biotic integrity (IBI), the Modified Index of Well-Being (MIWB) and the Invertebrate Community Index (ICI). These three indices are based on species richness, trophic composition, diversity, presence of pollution-tolerant individuals or species, abundance of biomass, and the presence of diseased or abnormal organisms. The IBI and the MIWB apply to fish; the ICI applies to macroinvertebrates. Ohio EPA uses the results of sampling reference sites to set minimum criteria index scores for use designations in water quality standards.

Provisions addressing biological criteria are in paragraph (C) of rule 3745-1-07 of the OAC.


The antidegradation provisions describe the conditions under which water quality may be lowered in surface waters. Existing beneficial uses must be maintained and protected. Further, water quality better than that needed to protect existing beneficial uses must be maintained unless lower quality is deemed necessary to allow important economic or social development (existing beneficial uses must still be protected).

Provisions addressing antidegradation are in rule 3745-1-05 and rule 3745-1-54 of the OAC.  Additional information is available at Antidegradation.

Public Participation

Any interested individuals can have a role in the process of developing water quality standards. Ohio EPA reviews and, as appropriate, revises water quality standards at least once every three years. When water quality standards revisions are proposed, the public is notified of these revisions. A public hearing is held to gather input and comments.

Water Quality Criteria & Values

Summary Tables

These tables summarize aquatic life and human health numerical water quality criteria and values contained in and developed pursuant to Chapter 3745-1 of the Ohio Administrative Code. The Lake Erie table was last updated on April 9, 2021. The Ohio River table was last updated on April 9, 2021.


Information about the Great Lakes Initiative, including the GLI Toxicity Data Clearinghouse, is on the U.S. EPA Great Lakes Initiative (GLI) Clearinghouse website.

Surface water quality criteria and procedures to calculate water quality criteria are contained in Chapter 3745-1 of the Ohio Administrative Code (OAC). With adoption of rules in 1997 pursuant to the federal Great Lakes Initiative, the water quality criteria for many chemicals differ between the Lake Erie drainage basin and the Ohio River drainage basin. The Lake Erie drainage basin comprises roughly the northern third of Ohio. The Ohio River drainage basin comprises the rest of the state.

The numerical human health water quality criteria are in rule 3745-1-33 (public water supply) and rule 3745-1-34 (fish consumption). The numerical aquatic life and wildlife water quality criteria and other types of numerical water quality criteria are in rule 3745-1-35.  Criteria to protect the recreation use (E. coli) and aesthetic conditions are found in rule 3745-1-37. These rules are available here:

  • 3745-1-33 Water quality criteria for water supply use designations      
  • 3745-1-34 Water quality criteria for the protection of human health [fish consumption]      
  • 3745-1-35 Aquatic life and wildlife criteria
  • 3745-1-37 Water quality criteria for recreation use designations and aesthetic conditions

In addition to the numerical criteria in the rules, there are procedures allowing the calculation of additional water quality criteria. These procedures are in the following rules.

  • 3745-1-40 Methodologies for development of aquatic life criteria and values
  • 3745-1-42 Methodologies for development of human health criteria and values for the Lake Erie drainage basin
  • 3745-1-43 Methodology for development of wildlife criteria for the Lake Erie drainage basin

Triennial Review


What are Water Quality Standards?

Water quality standards (WQS) are state regulations or rules that protect lakes, rivers, streams and other surface water bodies from pollution. These rules contain beneficial use designations such as warmwater aquatic life habitat, public water supply and primary contact recreation, water quality criteria (numeric levels and narrative statements) protective of the beneficial use designations, and procedures for applying the water quality criteria to discharges. WQS are the foundation for other regulatory actions such as permitting, compliance, enforcement, and monitoring and assessing the quality of Ohio’s waters.

Water Quality Standards are comprised of three elements:

  • Use Designations – water supply, recreation, fish and wildlife
  • Water Quality Criteria – narrative and numeric criteria and values derived from methods described in rule
  • Antidegradation Policy – keep clean water clean

Where can I find Ohio’s Water Quality Standards?

Ohio’s water quality standards are found in Ohio Administrative Code (OAC) 3745-1.

What is the Triennial Review?

The Ohio Environmental Protection Agency’s Division of Surface Water is conducting a Triennial Review of Ohio’s Water Quality Standards, a process required by the federal Clean Water Act (40 CFR 131.20). This review helps keep states’ WQS up to date by integrating the latest science, technology, policy, and federal requirements. The Triennial Review is an essential process in fulfilling the role of the federal Clean Water Act and provides an opportunity for public input to help the Agency determine and prioritize updates to the WQS.  It is important to note that while the Triennial Review process helps determine WQS priorities, it is not a rulemaking, rather it helps to guide the Agency for future rulemaking priorities. The Triennial Review has previously been conducted through rulemaking procedures. However, Ohio EPA is decoupling the Triennial Review from the rulemaking process and is implementing the new process described below.

NOTE: Only topics related to Water Quality Standards are considered for Triennial Review. Topics related to implementation are not considered.

New Triennial Review Process

Step 1: Internal Review and Draft Prioritization of WQS Projects

The Division of Surface Water will solicit internal Agency staff for input on surface water quality standards that may need review or revision in the next three years. Based on these suggestions, rule review schedules, new information, and program/division needs, the Division will create a draft ranking of WQS updates. 

Step 2: Public Comment Period

Ohio EPA will solicit input from the public on WQS priorities during a 60-day public comment period. The public may also suggest topics not included on the draft priority list. Ohio EPA will hold a public hearing to solicit verbal comments and answer any questions about the WQS priorities or the Triennial Review process.

Step 3: Review and Consideration of Comments Received

Comments received during the public comment period and public hearing will be reviewed and considered by Agency WQS staff when prioritizing WQS updates. A draft workplan for the upcoming three years will be developed.

Step 4: Report Out

The Agency will report out on the final WQS topics for prioritization after it has finalized its review. This document will include:

  • A summary of the Triennial Review process
  • The final workplan for the next three years
  • Responses to comments 
  • Please note that the Agency will not be responding to individual comments. Instead, the report will summarize suggested priorities and provide justifications for selected WQS  changes and a rationale for those we are not pursuing during this Triennial Review period. 
  • This report will be made publicly available and posted on Ohio EPA’s Triennial Review webpage. An email notification will be sent to the Ohio EPA DSW’s Rulemaking listserv to notify stakeholders of the end of the review process.  

Step 5: Work on Priority Projects

Ohio EPA will proceed with rulemaking on the prioritized WQS as outlined in the Triennial Review workplan.