Assessment Comments
Assessment remains based on occurrence of a fish kill in July 2002.
Basis for Assessment
SUMMARY: The Class B(CW) aquatic life uses remain assessed (evaluated) as "partially supported" due to occurrence of a fish kill in July 2002. This cause of this kill remains “unknown.” This is the same assessment as that developed for the 2004 assessment/listing cycle. The continuance of the IR Category 3b listing is based on IDNR's 2006 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 (2002-2005) 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.
EXPLANATION: The fish kill occurred on July 24, 2002. No cause was determined; the kill occurred after a rainfall event that followed a period of hot, dry weather. Approximately 1.5 miles of stream was affected, and an estimated 2,500 fish were killed. According to IDNR's assessment methodology for Section 305(b) reporting, occurrence of a single pollution-caused fish kill within the most recent three-year period indicates ongoing impairment of the aquatic life uses.
According to IDNR’s assessment methodology, if a cause of a fishkill was not identified during the IDNR investigation (= "unknown"), 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 (Category 5 of the Integrated Report). Waterbodies affected by such fish kills will be placed in IR subcategories 2b or 3b and thus will be added to the state’s list of “waters in need of further investigation”.
