Assessment Comments
Assessment is based on results of a fish kill investigation in June 2006.
Basis for Assessment
SUMMARY: The Class B(LW) (aquatic life) uses of Griswold Park Pond are assessed (evaluated) as "partially supported" due to a fish kill in June 2006. The fish consumption uses remain "not assessed" due to a lack of fish contaminant monitoring at this lake.
EXPLANATION: The Class B(LW) (aquatic life) uses are assessed (evaluated) as "partially supported" due to a fish kill in June 2006. The kill occurred on or before June 21, 2006 and was attributed to natural causes (low dissolved oxygen due to an algal die-off). Approximately 1260 fish were killed including: 1249 bluegill, 6 largemouth bass, 3 grass carp, 2 channel catfish, and numerous young-of year bluegill and largemouth bass. Low oxygen conditions were likely caused by the treatment of the lake with copper sulfate to control algae on June 21, 2006. This along with high water temperatures (approaching 90 ○F) likely caused low oxygen levels. It is likely that low oxygen conditions existed during the evening of June 22 to the morning of June 23. Dead and struggling fish were observed on the morning of June 23. By the afternoon of June 23, oxygen readings ranged from 4-10 ppm throughout the pond and no additional dead fish were observed during subsequent visits. It was noted that young-of-the-year fish may also have died from toxic levels of copper following the application. The value of dead fish was estimated to be $ 19,112.40.
According to IDNR’s assessment/listing methodology, 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 (2004-2007) 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.” Such assessments, although suitable for Section 305(b) reporting, lack the degree of confidence to support addition to the state Section 303(d) list of impaired waters (IR Category 5). Waterbodies affected by such fish kills 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 3b of Iowa’s 2008 Integrated Report.
Fish consumption uses remain "not assessed" due to a lack of fish contaminant monitoring at this lake.
