Assessment Comments
Assessment remains based on results of U.S. EPA/IDNR fish contaminant monitoring in 2011.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses and the Class B(WW1) aquatic life uses remain "not assessed" (IR 3a) due to lack of water quality information upon which to base an assessment. The fish consumption (Class HH) uses remain assessed (monitored) as "partially supported" (IR 5a) due to issuance of fish consumption advisory. The source of data for this assessment is the results of U.S. EPA/Iowa DNR fish contaminant (RAFT) monitoring near Clarksville in September 2011.
EXPLANATION: The fish consumption uses remain assessed (monitored) as “partially supported” based on results of U.S.EPA/IDNR fish contaminant (RAFT) monitoring in 2011. The existence of, or potential for, a fish consumption advisory is the basis for Section 305(b) assessments of support of fish consumption uses in Iowa’s rivers and lakes. The fish contaminant data generated from the 2011 RAFT sampling conducted on the Shell Rock River near Clarksville showed that levels of mercury are sufficiently high for concern and thus justified issuance of a one meal/week fish consumption advisory in 2013 that extends from the mouth of the Shell Rock River to its confluence with the Winnebago River near Rockford in Floyd County. Results from the 2011 sampling showed that the level of mercury in the sample of walleye muscle tissue (0.75 ppm) far exceeds the 1 meal/week trigger level (0.30 ppm) as defined in Iowa’s revised (2007) fish consumption advisory protocol. According to the Iowa DNR/Iowa Dept. of Public Health fish advisory protocol, the single occurrence of contaminant above an advisory trigger level does not typically result in issuance of an advisory. Such an advisory is issued only after follow-up monitoring confirms that contaminant levels exceed the advisory trigger level. Because, however, the level of mercury in the 2011 sample of walleye was well above the one meal/week advisory trigger, a one meal/week consumption advisory was issued. Follow-up monitoring will be conducted to better define the level of mercury in Shell Rock River fish and to provide information for any changes needed to the consumption advisory. Because a one meal per week fish consumption advisory was issued for this waterbody, the fish consumption uses are assessed as “partially supported.”
