Assessment Comments
Assessment remains based on results of U.S. EPA/IDNR fish tissue (RAFT) monitoring in 2002, 2005, 2006, 2008, and 2012 near Decorah.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses and the Class B(WW1) aquatic life uses remain "not assessed" due to the lack of information upon which to base an assessment. Fish consumption uses remain assessed (monitored) as “partially supported” (IR 5a) based on results of fish contaminant monitoring near Decorah and issuance of a "one meal per week" consumption advisory. The source of data for this assessment is the results of U.S. EPA/IDNR fish tissue (RAFT) monitoring in 2002, 2005, 2006, 2008 and 2012 near Decorah.
EXPLANATION: Fish consumption uses remain assessed (monitored) as “partially supported” based on results of U.S.EPA/IDNR fish contaminant (RAFT) monitoring upstream from Decorah and on the issuance of a fish consumption advisory in 2006. 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. This scenario applies to the fish contaminant data generated from the RAFT sampling conducted in this segment of the Upper Iowa River: levels of mercury in samples of smallmouth bass from consecutive samplings exceeded advisory trigger levels, thus suggesting the need for a consumption advisory. According to IDNR’s assessment methodology, the existence of a one-meal/week consumption advisory indicates that fish consumption uses should be assessed as “partially supported”.
For the 2002 RAFT sampling, the composite samples of fillets from common carp and smallmouth bass had generally low levels of contaminants. Levels of primary contaminants in the composite sample of common carp fillets were as follows: mercury: 0.036 ppm; total PCBs: <0.09 ppm; and technical chlordane: <0.03 ppm. Levels of primary contaminants in the composite sample of smallmouth bass fillets were as follows: mercury: 0.334 ppm; total PCBs: <0.09 ppm; and technical chlordane: <0.03 ppm. The level of mercury in the sample of smallmouth bass (0.0.334 ppm), however, exceeded the IDNR/IDPH trigger level of 0.30 ppm for a one meal per week consumption advisory (this levels is well below the “do not eat” trigger level for mercury of 1.0 ppm).
For the 2005 RAFT sampling, levels of primary contaminants in the composite sample of common carp fillets were as follows: mercury: 0.036 ppm; total PCBs: <0.09 ppm; and technical chlordane: <0.03 ppm. Levels of primary contaminants in the composite sample of smallmouth bass fillets were as follows: mercury: 0.334 ppm; total PCBs: <0.09 ppm; and technical chlordane: <0.03 ppm. Similar to the 2002 sampling, the level of mercury in the smallmouth bass fillets at this site exceeded the IDNR/IDPH trigger level of 0.3 ppm.
The 2006 RAFT sampling produced similar results. The composite sample of smallmouth bass fillets contained 0.32 ppm of mercury. The sample of golden redhorse (Moxostoma erythrurum) fillets contained 0.567 ppm of mercury. Both of these levels were above the 0.3 one-meal/week advisory trigger level.
Follow-up fish contaminant monitoring was conducted in this river segment in 2008 as part of the RAFT program. Similar to results from the 2006 RAFT, the level of mercury in the sample of golden redhorse fillets (0.351 ppm) exceeded the IDNR/IDPH trigger level, thus confirming the need for continuance of the 1 meal per week consumption advisory issued in 2008. Because the levels of mercury in samples of smallmouth bass fillets from this river segment consistently have been at or above the advisory trigger level, a one-meal/week advisory was issued by IDNR and IDPH in January 2006. This advisory originally covered the reach of the Upper Iowa River from the Lower Dam in eastern Winneshiek County to the county road bridge approximately 5.5 miles upriver (northwest) from Decorah. Additional fish contaminant (RAFT) monitoring in 2006 resulted in extending this advisory March 2008 to downriver from the Lower Dam to state highway 76.
Results of RAFT follow-up monitoring in 2012 showed lower levels of mercury in smallmouth bass. The average level of mercury in the muscle tissue samples from three smallmouth bass was 0.179 ppm (standard deviation of 0.036 ppm); this average is well below the advisory threshold of 0.3 ppm. According to the IDNR/IDPH advisory protocol, however, two consecutive samplings showing that contaminant levels are below the advisory threshold are needed to rescind a consumption advisory. Thus follow-up fish tissue monitoring will be conducted in this assessment segment to determine whether levels of mercury in smallmouth bass have declined and whether the consumption advisory should be rescinded.
