Assessment Comments
Assessment is based on results of a fish kill investigation in August 2007.
Basis for Assessment
SUMMARY: The Class B(LW) aquatic life uses of this waterbody are assessed (evaluated) as “partially supported” due to a fish kill in August 2007. The kill was attributed to natural causes. This impairment is appropriate for Category 3b of Iowa’s 2006 Integrated Report. The fish consumption uses are "not assessed" due to lack of fish contaminant data upon which to base an assessment.
EXPLANATION: The fish kill occurred on or before August 16, 2007. The kill was attributed to unknown causes, however human causes were suspected. The kill claimed 922 fish, including 710 crappie, 198 bluegill, seven bullheads and seven green sunfish; no estimate of the value of these fish was made.
The DNR plans to continue to investigate the source, which may be a substance from Harlan’s storm sewer. A storm sewer outfall from the City of Harlan sends storm water into Little Lake George without treatment. While high water temperatures can stress fish during summer months, samples collected at the lake by DNR staff showed high levels of dissolved oxygen, indicating the fish kill was likely caused by a pollutant.
According to the IDNR 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 (2004-2006) 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.
The fish consumption uses are "not assessed" due to lack of fish contaminant data upon which to base an assessment.
