Assessment Comments
Assessment is based on (1) results of a fish kill investigation on August 3, 2006, and (2) results of U.S. EPA/IDNR fish contaminant (RAFT) monitoring in 2007.
Basis for Assessment
SUMMARY: The Class B(LW) (aquatic life) uses are assessed (evaluated) as “partially supported” due to a fish kill in August 2006. The kill was attributed to natural causes. This impairment is appropriate for Category 3b of Iowa’s 2010 Integrated Report. Fish consumption uses are assessed (monitored) as "fully supported." The sources of data for this assessment are (1) results of a fish kill investigation on August 3, 2006, and (2) results of U.S. EPA/IDNR fish contaminant (RAFT) monitoring in 2007.
EXPLANATION: The Class B(LW) aquatic life uses are assessed (evaluated as "partially supported" due to a fish kill in 2006. The fish kill occurred on or before August 3, 2006 and was attributed to natural causes (high temperatures and low dissolved oxygen). An estimated 20 fish were killed including small number of bass, northern and yellow bass. Anglers have observed live bluegill in the lake. No estimate of the value of the fish killed was provided.
This assessment was placed in Category 3b of Iowa's 2008 Integrated Report. Due to information of fish tissue this assessment is placed in IR Category 2b based on IDNR's 2010 assessment methodology that states the following: the occurrence of a single pollutant-caused fish kill, or a fish kill of unknown origin, on a waterbody or waterbody reach during the most recent assessment period (2006-2009) indicates a severe stress to the aquatic community and suggests that the aquatic life uses should be assessed as “impaired”. If a cause of the kill was not identified during the IDNR investigation, or if the kill was attributed to non-pollutant causes (e.g., winterkill), the assessment type will be considered “evaluated” and will be placed in IR subcategories 2b or 3b and will be added to the state list of waters in need of further investigation. Thus, this assessment segment will be placed in Category 2b of Iowa’s 2010 Integrated Report.
Fish consumption uses were assessed (monitored) as “fully supported” based on results of U.S. EPA/IDNR fish contaminant (RAFT) monitoring at Fisher Lake in 2007. The composite samples of fillets from common carp and largemouth bass had low levels of contaminants. Levels of primary contaminants in the composite sample of common carp fillets were as follows: mercury: 0.118 ppm; total PCBs: 0.09 ppm; and technical chlordane: <0.03 ppm. Levels of primary contaminants in the composite sample of largemouth bass fillets were as follows: mercury: 0.226 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 fish contaminant data generated from the 2007 RAFT sampling conducted at this lake show that the levels of contaminants do not exceed any of the advisory trigger levels, thus indicating no justification for issuance of a consumption advisory for this waterbody.
