Assessment Comments
Assessment is based on results of an IDNR investigation of a fish kill in August 2005.
Basis for Assessment
SUMMARY: The general uses of this stream are assessed (monitored) as “partially supported” due to a fish kill in August 2005. The kill was caused by ammonia from an unspecified source. The party responsible for the kill was not identified. This impairment is appropriate for Category 5b of Iowa’s 2006 Integrated Report (=Section 303(d) list).
EXPLANATION: This kill occurred on or before August 19, 2005; the cause of the kill was attributed to ammonia from a nonpoint/unspecified source. An estimated 80 fish were killed; no estimate of valuation of the fish killed was provided. No responsible party was identified. Comments from the investigation of the kill include the following: At the point of the fish kill, the water slows down and pools. The water was murky and brown with lots of algae, but no odor or foaming was observed. Levels of dissolved oxygen were greater than 15 ppm. The concentration of ammonia at site was 2.8 mg/L. Upstream, the ammonia concentration was 0.8 mg/L and downstream was 1.4 mg/L. No fish were seen upstream due to low flow, but the water was clear. Several minnows were observed downstream. No tile lines were observed feeding into the stream during the investigation.
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 (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 is identified, and the cause is either known, or suspected, to be a “pollutant”, the assessment type is considered “monitored” and the affected waterbody is a candidate for Section 303(d) listing. Fish kills attributed to a pollutant, but where a source of the pollutant was not identified, will be placed into Integrated Report subcategory 5b. The intent of placing these waterbodies into Category 5 is not to necessarily require a TMDL but to keep the impairment highlighted due to the potential for similar future kills from the unaddressed causes and/or sources.
