Assessment Comments
Assessment is based on results of (1) DNR/UHL biocriteria sampling in 1998 and (2) U.S. EPA/IDNR fish tissue (RAFT) monitoring at Pammell Park in 2002.
Basis for Assessment
SUMMARY: The Class B(WW) aquatic life uses are assessed (monitored) as "fully supported/threatened" (minor impacts) based on results of biological monitoring in 1998. Fish consumption uses are assessed (monitored) as "fully supported" based on results of fish contaminant monitoring in 2002. Sources of data for this assessment include (1) results of IDNR/UHL biological monitoring conducted in 1998 as part of the stream biocriteria project, (2) a report of a fish kill on July 20, 2002, and (3) results of U.S. EPA/IDNR fish contaminant (RAFT) monitoring in 2002.
EXPLANATION: The Class B(WW) aquatic life uses remain assessed as "fully supported / threatened" based on results of IDNR/UHL biological monitoring conducted on this stream segment in 1998 (see assessment for the 2000 report). These data are less than five years old and, according to IDNR's methodology for Section 305(b) assessments, are thus appropriate for characterizing current water quality conditions. A fish kill occurred in this river segment on July 20, 2002 near the Middle River Park south of Winterset. This kill is believed due to warm water temperatures, low river flow, and the die-off of an algae bloom that reduced levels of dissolved oxygen below that needed to sustain large fish. At the time of the kill, levels of dissolved oxygen were in the vicinity of 3 mg/l; the water was brownish, probably due to the senescence of the algal bloom. Because this kill is largely due to natural causes (low flow; high water temperatures), the kill does not influence the assessment of support of the designated aquatic life uses of this stream segment. Fish consumption uses are assessed (monitored) as "fully supported" based on results of U.S. EPA / IDNR fish tissue (RAFT) monitoring in 2002. The composite samples of fillets from channel catfish and walleye had very low levels of contaminants. Neither sample contained levels of contaminants that approached even one-half the respective FDA action levels or IDNR levels of concern. Levels of primary contaminants in the composite sample of channel catfish fillets were as follows: mercury: 0.142 ppm; total PCBs: <0.09 ppm; and technical chlordane: <0.03 ppm. Levels of primary contaminants in the composite sample of walleye fillets were as follows: mercury: 0.184 ppm; total PCBs: <0.09 ppm; and technical chlordane: <0.03 ppm.
