Assessment Comments
Assessment remains based on (1) surveys of Nebraska fisheries biologists and consultation with IDNR staff and (2) U.S. EPA/IDNR fish tissue (RAFT) monitoring in 2007.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses remain “not assessed” due to the lack of data upon which to base an assessment. This segment was incorrectly identified by IDNR as impaired by bacteria on Iowa’s 2006 Section 303(d) list. This incorrectly-identified impairment was de-listed during the 2008 Integrated Reporting cycle. The Class B(WW1) aquatic life uses remain assessed (evaluated) as "partially supported" based on information from local fisheries biologists on impacts related to flow modification and habitat alterations in this segment of the Missouri River. The fish consumption uses are assessed (monitored) as "fully supported" based on results of fish contaminant monitoring in 2007. The sources of information for this assessment include (1) results of U.S. EPA/IDNR fish tissue (RAFT) monitoring near Nebraska City in September 2007 and (2) information from Nebraska fisheries biologists.
EXPLANATION: The Class A1 (primary contact recreation) uses remain “not assessed.” The previous (2006) bacterial impairment identified for this river segment by IDNR was incorrectly based on data collected by the Nebraska Department of Environmental Quality. These data were collected approximately 60 miles downriver from the Iowa state line; thus, the data are of questionable relevance to bacterial levels in Iowa DNR's Missouri River assessment segment IA 06-WEM-0010_0.
The Class B(WW1) aquatic life uses remain assessed (evaluated) as "partially supported" based on the assessment developed for previous reporting cycles (i.e., habitat alterations and flow modifications that resulted from development of the river for navigation uses in the mid-Twentieth Century). This impairment is appropriate for Integrated Report Category 4c (impairment is not caused by a pollutant). This assessment was developed in consultation with the Missouri River fisheries biologist for the state of Nebraska.
Fish consumption uses remain assessed (monitored) as “fully supported” based on results of U.S.EPA/IDNR fish contaminant (RAFT) monitoring near Nebraska City in 2007. The composite samples of fillets from channel catfish and flathead catfish had low levels of contaminants. Levels of primary contaminants in the composite sample of common carp fillets were as follows: mercury: 0.126 ppm; total PCBs: 0.09 ppm; and technical chlordane: 0.03 ppm. Levels of primary contaminants in the composite sample of flathead catfish fillets were as follows: mercury: 0.113 ppm and total PCBs: 0.09 ppm. The existence of, or potential for, a fish consumption advisory is the basis for Section 305(b) assessments of the degree to which Iowa’s lakes and rivers support their fish consumption uses. The levels of contaminants did not exceed any of the Iowa's advisory trigger levels, thus suggesting no justification for issuance of a consumption advisory for this waterbody and "full support" of the fish consumption uses.
