Assessment Comments
Assessment is based on results of a fish kill investigation in June 2009.
Basis for Assessment
[Note: Prior to the 2008 Section 305(b) cycle, this stream segment was designated only for Class B(LR) aquatic life 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. The stream remains designated for aquatic life uses (now termed Class B(WW2) aquatic life uses). Thus, for the current (2010) assessment, the available water quality monitoring data will be compared to the applicable Class A1 and Class B(WW2) water quality criteria.]
SUMMARY: The Class A1 (primary contact recreation) uses are "not assessed" due to a lack of information upon which to base an assessment. The Class B(WW2) aquatic life uses are assessed (monitored) as "partially supported" based on results of a fish kill investigation in June 2009.
EXPLANATION: The kill occurred on or before June 8, 2009 and affected an unknown, but small number of fish. While the number of fish killed was small, the value of the fish was high, as many trout were killed. The kill occurred along a 4.5 mile stretch of Buck Creek one mile NNW of Garnavillo. The cause of the kill was suspected to be of human origin, as there was a recent pesticide spill to the stream and the potential from runoff from an open cattle feed lot.
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 (2007-2009) 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 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 and/or where enforcement actions were not taken against the responsible party, 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. Thus, this assessment segment will be placed in Category 5b of Iowa’s 2010 Integrated Report.
