Assessment Comments
Assessment is based on results of water quality monitoring from June 2011 to August 2012 by USGS at Nebraska City (station 06807000), and this assessment remains based on results of (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” (IR 3a) due to the lack of data upon which to base an assessment. The Class B(WW1) aquatic life uses remain assessed (evaluated) as "partially supported" (IR 4c) 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 remain assessed (monitored) as "fully supported" (IR 2a) based on results of fish contaminant monitoring in 2007. The sources of information for this assessment include (1)results of USGS water quality monitoring at Nebraska City from June2011 to August 2012, (2) results of U.S. EPA/IDNR fish tissue (RAFT) monitoring near Nebraska City in September 2007 and (3) information from Nebraska fisheries biologists.
EXPLANATION: The Class A1 (primary contact recreation) uses remain “not assessed.” Water quality monitoring conducted by USGS at Nebraska City from 2010-12 did not include monitoring for indicator bacteria.
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.
Results of limited water quality monitoring conducted by USGS at Nebraska City from June 2011 to August 2012 showed no violations of Class B(WW1) criteria for dissolved oxygen (minimum value = 5.2 mg/l) or pH (range = 7.9 to 8.4 units in the 16 samples collected. In addition, there were no violations of the Class B(WW1) criterion for temperature in the 284 samples collected between January 19, 2010 and December 18, 2012 (maximum = 31C). Thus, these results do not suggest chemical/physical water quality problems in this segment of the Missouri River.
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.
