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
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.
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:
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.