Assessment Comments
Assessment is based on results of fish kill investigations in April 2005 and August 2006.
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 April 2005 and a fish kill in August 2006. Both kills were attributed to natural causes. This impairment is appropriate for Category 3b of Iowa’s 2006 Integrated Report. The primary contact recreation and fish consumption uses are "not assessed" due to lack of data upon which to base an assessment.
EXPLANATION: The first kill occurred on or before April 14, 2005. The kill was attributed to “unknown/natural” causes. IDNR field staff investigated this kill. An estimated 30 fish were killed (all largemouth bass); no estimate of the value of the fish killed was provided. The dead largemouth bass were found from west of the beach to the northwest boat launch. Most of the bass were about 6 inches long; a few were up to 9 inches, and a couple were about 2 inches in length. A light wind was blowing from the southeast and likely concentrated the dead fish at this end of the lake. Water quality testing did not identify any obvious causes of the kill. The IDNR Fisheries Bureau suggested that the kill could have been caused by a virus or may have even resulted from winterkill.
The second fish kill occurred on or before August 16, 2006. The kill was attributed to "unknown/natural" causes. The total number of fish killed was 89. The estimated value of these fish was $589.94. No evidence was found to indicate the cause of this fish kill.
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 (2004-2007) 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.
The fish consumption uses are "not assessed" due to lack of fish contaminant data upon which to base an assessment.
