Water quality criteria are numeric or narrative guidelines that protect or support a designated use. These criteria are expressed as either concentrations (for example, milligrams per liter) or as narrative statements. If water quality criteria are met, the level of water quality will generally protect the designated use.

The information below is summary of specific chemical water quality criteria published in Environmental Protection Rule 567, Chapter 61, "Water Quality Standards."

Class "A" Waters: Waters which are designated as Class “A1,” “A2,” or “A3” in subrule 61.3(5) are to be protected for primary contact, secondary contact, and children’s recreational uses. The general criteria of subrule 61.3(2) and the following specific criteria apply to all Class “A” waters.

1. The Escherichia coli (E. coli) content shall not exceed the levels noted in the Bacteria Criteria Table when the Class “A1,” “A2,” or “A3” uses can reasonably be expected to occur.
   
   

   Use	Geometric Mean	Sample Maximum
   Class A1
   3/15 - 11/15	126	235
   11/16 - 3/14	Does not apply	Does not apply
   Class A2 (Only)
   3/15 - 11/15	630	2880
   11/16 - 3/14	Does not apply	Does not apply
   Class A2 and B(CW) or HQ
   Year Round	630	2880
   Class A3
   3/15 - 11/15	126	235
   11/16 - 3/14	Does not apply	Does not apply
   Class A1 – Primary Contact Recreational Use Class A2 - Secondary Contact Recreational Use Class A3 – Children’s Recreational Use

   
   
   
2. The pH shall not be less than 6.5 nor greater than 9.0. The maximum change permitted as a result of a waste discharge shall not exceed 0.5 pH units.

Class "B" Waters: All waters which are designated as Class B(CW), B(WW), B(LR), or B(LW) are to be protected for wildlife, fish, aquatic and semiaquatic life uses. The following criteria shall apply to all Class "B" waters designated in subrule 61.3(5).

1. Dissolved oxygen. Dissolved oxygen shall not be less than the values shown here:
   
   

   	B(CW)	B(WW)	B(LR)	B(LW)
   Minimum value for at least 16 hours of every 24-hour period	7.0 mg/l	5.0 mg/l	5.0 mg/l	5.0* mg/l
   Minimum value at any time during every 24-hour period	5.0 mg/l	5.0 mg/l	4.0 mg/l	5.0*mg/l

   * Applies only to the upper layer of stratification in lakes
   
   
2. pH. The pH shall not be less than 6.5 nor greater than 9.0. The maximum change permitted as a result of a waste discharge shall not exceed 0.5 pH units.
   
   
3. General chemical constituents. The specific numerical criteria shown in Tables 1, 2, and 3 of this subrule apply to all waters designated in subrule 61.3(5). The sole determinant of compliance with these criteria will be established by the department on a case-by-case basis. Effluent monitoring or instream monitoring, or both, will be the required approach to determine compliance.
   
   
   • Table 1, Criteria for Chemical Constituents (*.pdf file)
   • Table 2, Criteria for Dissolved Oxygen (*.pdf file)
   • Table 3a, Acute Criterion for Ammonia in Iowa Streams (*.pdf file)
   • Table 3b, Chronic Criterion for Ammonia in Iowa Streams – Early Life Stages Present (*.pdf file)
   • Table 3c, Chronic Criterion for Ammonia in Iowa Streams – Early Life Stages Absent (*.pdf file)
   
   
   
4. The waters shall contain no substances in concentrations which will make fish or shell-fish inedible due to undesireable tastes or cause a hazard to humans after consumption. Specific toxic chemical criteria are listed in 567.61.3(3), Table 1.
   
   
5. Temperature.
   
   
6. Early life stage for each use designation.

Class "C" Waters: Waters which are designated as Class "C" are to be protected as a raw water source of potable water supply. The following criteria shall apply to all Class "C" waters designated in subrule 61.3(5).

1. Radioactive substances.
   • The combined radium-226 and radium-228 shall not exceed 5 picocuries per liter at the point of withdrawal.
   • Gross alpha particle activity (including radium-226 but excluding radon and uranium) shall not exceed 15 picocuries per liter at the point of withdrawal.
   • The average annual concentration at the point of withdrawal of beta particle and photon radioactivity from man-made radionuclides other than tritium and strontium-90 shall not produce an annual dose equivalent to the total body or any internal organ greater than 4 millirem/year.
   • The average annual concentratuion of tritium shall not exceed 20,000 picocures per liter at the point of withdrawal; the average annual concentration of strontium-90 shall not exceed 8 picocuries per liter at the point of withdrawal.
2. All substances toxic or detrimental to humans or detrimental to treatment process shall be limited to nontoxic or nondetrimental concentrations in the surface water. Specific toxic chemical criteria are listed in 567.61.3(3), Table 1.
3. The pH shall not be less than 6.5 nor greater than 9.0.

• Table 1, Criteria for Chemical Constituents (*.pdf file)
• Table 2, Criteria for Dissolved Oxygen (*.pdf file)
• Table 3a, Acute Criterion for Ammonia in Iowa Streams (*.pdf file)
• Table 3b, Chronic Criterion for Ammonia in Iowa Streams – Early Life Stages Present (*.pdf file)
• Table 3c, Chronic Criterion for Ammonia in Iowa Streams – Early Life Stages Absent (*.pdf file)