Assessment Comments
Assessment remains based on results of IDNR fish kill investigations in July 2005 and August 2006.
Basis for Assessment
[Note: Prior to the 2008 Section 305(b) cycle, this stream segment was classified only for Class B(LR). Due to changes in Iowa’s surface water classification that were approved by U.S. EPA in February 2008, this segment is now presumptively designated for Class A1 (primary contact recreation) uses and for Class B(WW2) aquatic life uses. Thus, for the current (2012) assessment the available water quality monitoring data will be compared to the applicable Class A1 and Class B(WW2) water quality criteria.]
SUMMARY: The presumptive Class A1 (primary contact recreation) uses remain "not assessed" due to a lack of water quality information upon which to base an assessment. The Class B(WW2) aquatic life uses of this waterbody remain assessed (monitored) as “partially supported” due to fish kills in July 2005 and August 2006.
EXPLANATION: The most recent kill occurred on or before August 20, 2006 and was attributed to manure runoff. The kill affected approximately 2.52 miles of Lake Creek on the northeast edge of Rockwell City. An estimated 6,555 fish were killed, although live fish were observed in the stream. The estimated value of the fish was $651.37. The party responsible for the kill was identified, and restitution was sought. NOTE: This assessment was placed in Category 5b of the 2008 Integrated Report due to a lack of information on whether or not restitution was sought for this fish kill. Due to updated information regarding legal action, this assessment was placed in Category 4d of Iowa's 2010 Integrated Reporting cycle and remains in Category 4d for the current (2012) reporting cycle.
According to DNR's assessment methodology for Section 305(b) reporting, occurrence of a single pollution-caused fish kill during an assessment period indicates "partial support" of the aquatic life uses. If, however, a consent order has been issued to the party responsible for the kill and monetary restitution has been sought for the fish killed, the affected waterbody should be placed in IR Category 4d (impaired but TMDL not required). IDNR considers IR 4d fish kill waters with no subsequent kills in at least the five years subsequent to the kill as appropriate for movement to IR categories 2b or 3b (i.e., Iowa’s list of waters in need of further investigation). Because, however, this fish kill occurred within the most recent five years, this assessment segment will remain in Category 4d of Iowa’s Integrated Report.
The second kill on this segment occurred on or before July 18, 2005 and was attributed to natural causes (water temperature). Approximately 3 miles of stream were affected. Results of the IDNR investigation show that levels of dissolved oxygen were high and levels of ammonia were very low. The kill was attributed to water temperatures that remained in the upper 70s (F) despite a recent rainfall event. The kill affected nongame species; no estimate of the number of fish killed was provided. The observation of live fish suggested that this was only a partial kill. Although believed unrelated to the kill, the Rockwell City area received from 1 to 2-inches of rainfall the evening prior to the kill.
