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Fish Kill Monitoring and Reporting

 In the past few years, fish kills have become a focus of public attention as more interest is being placed on the quality and condition of Iowa's streams and rivers.

The advent of 305(b) reporting and Impaired Waters Listings caused the TMDL and Water Quality Assessment section to begin tracking fish kills and their causes to a greater degree than before. A fish kill can affect the 305(b) water quality assessment of the waterbody, and can potentially cause the waterbody to be listed on the 303(d) listing of impaired waters.

From 1999 to 2001, the Iowa Department of Natural Resources (IDNR) and University Hygienic Laboratory (UHL) sampled fish communities in 23 streams that were affected by major fish kills. The primary goal of the project was to assess the status of biological conditions in fish kill streams and evaluate recovery of fish populations. The final report of this project is available online.

Fish Kills and Water Quality

As described in Iowa DNR's current methodology for water quality assessments, occurrence of a single pollutant-caused fish kill, or a fish kill of unknown origin, on a waterbody or portion of a waterbody during the most recent three-year period indicates an impairment of the aquatic life uses. This "once in three-year" frequency of criteria violation is designed to provide protection for ecological recovery from a severe stress and is consistent with U.S. EPA recommendations (U.S. EPA 1994: page 3-3).

Each report of a fish kill will be reviewed to determine whether development of a TMDL is appropriate. In the absence of an ongoing source of a pollutant, TMDLs will not be developed for kills caused by a one-time illegal or unauthorized release of manure or other toxic substance. Impacts from this type of fish kill are addressed through IDNR's enforcement procedures. Fish kills attributed to authorized discharges (i.e., a discharge meeting permit limits) are considered for Section 303(d) listing as the existing, required pollution control measures are not adequate to address this impairment.

More information on the role of fish kills in the water quality assessment process can be found at:

Reporting a Fish Kill

If you believe a fish kill has occurred, please contact the nearest DNR Field Office or Fisheries Office. You should have available the name of the stream, the location of the kill, and any other conditions or observations that may aid in the investigation of the cause and source of the kill.

Fish Kill Data Available Online


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