Assessment Comments
Assessment is based on results of a fish kill investigation in July 2009.
Basis for Assessment
Note: Prior to the 2008 Section 305(b) cycle, this stream segment was classified only for general uses. Due to changes in Iowa’s surface water classification that were approved by U.S. EPA in February 2008 (see http://www.iowadnr.com/water/standards/files/06mar_swc.pdf), this segment is now presumptively designated for Class A1 (primary contact recreation) uses and for Class B(WW1) aquatic life uses. According to the Iowa Water Quality Standards, all perennial rivers and streams and all intermittent streams with perennial pools that are not specifically listed in the Iowa surface water classification are designated as Class A1 and Class B(WW1) waters. Thus, for the current (2010) assessment, perennial flow is presumed, and the available water quality monitoring data will be compared to the applicable Class A1 and Class B(WW1) water quality criteria.]
SUMMARY: The presumptive Class A1 (primary contact recreation) uses are "not assessed" based on a lack of information upon which to base an assessment. The presumptive Class B(WW-1) aquatic life uses are assessed (evaluated) as "partially supported" due to the occurrence of a fish kill in July 2009.
EXPLANATION: The fish kill event occurred prior to July 11, 2009. Approximately 320 fish were killed along 1.2 miles of Snag Creek. It was estimated that the kill occurred at least 48 hours prior to the investigation and high water occurred during, or after, the kill event. It is probable that high water flows flushed a significant number of dead fish from the investigated area, and decay and predation further reduced counts of small-bodied fishes. The value of the fish was estimated to be $4028.04. Live fish, including bluegill, were observed during the kill investigation. No cause for the kill was identified.
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 (2006-2009) 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 2010 Integrated Report.
