Assessment Comments

Assessment is based on results of a fish kill investigation on April 19, 2006.

Basis for Assessment

The Class B(WW1) (aquatic life) uses are assessed (evaluated) as "partially supported" due to a fish kill in April of 2006.   The kill occurred on or before April 19, 2006; no cause of the kill was identified.   Approximately 24 dead fish were observed in a pool on the Wapsipinicon River.   The species of fish could not be identified due to the level of decay.   Levels of ammonia in the water were below the detection limit.   Dissolved oxygen concentrations were greater than 10 mg/L and the temperature was 48 ○F.   No estimate of the value of the fish was developed.

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.