Assessment Comments
Assessment remains based on results of an IDNR investigation of a fish kill in September 2003 and on results of IDNR fish kill follow-up sampling in August 2011.
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, 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 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 remain "not assessed" (IR 3a) due to the lack of information upon which to base an assessment. The assessment of the presumptive Class B(WW1) aquatic life uses remains “not assessed” (IR 3a). This assessment reflects the change for the 2012 IR cycle from “partially supporting” (IR Category 5b) due to a 2003 fish kill to “not assessed” based on the results IDNR fish kill follow-up monitoring in 2011.
EXPLANATION: This fish kill occurred on or before September 16, 2003; the kill was attributed to ammonia from an unspecified/unknown source. An estimated 75 fish (unspecified species) were killed; no estimate of the value of the fish killed was provided. No responsible party was identified. The kill occurred near the intersection of highways 4 and 141; the location point for the kill is Section 17 of T81N, R30W, Guthrie County. According to the IDNR investigation, staff was unable to locate a definite source of the ammonia contributions to Mosquito Creek. IDNR staff reported the following levels of ammonia during the investigation: approximately 10 ppm at a location 3 to 4 miles southeast of Bagley; approximately 15-20 ppm 1 mile southeast of Bagley; 7.5 ppm at the outfall of the Bagley wastewater treatment plan. IDNR staff found very low concentrations of ammonia upstream from Bagley but felt that the lateness of the investigation may have allowed previously-high concentrations to decrease.
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 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.
This stream segment’s fish community was sampled on August 3, 2011, as part of the IDNR Watershed Improvement and Water Monitoring sections’ fishkill follow up monitoring program. Sampling methods described in IDNR’s fish kill follow-up protocol (Attachment 5 of Iowa’s 2012 assessment/listing methodology) were followed. Approximately 750 feet of stream were sampled using a single pass with one backpack electro-fishing unit. Results of this sampling showed that this stream supports approximately 3,100 fish per mile compared to the Level IV ecoregion 47b average of approximately 2,300 fish per mile; 82% of the expected fish taxa for this ecoregion were sampled. For detailed results of this sampling, see Iowa’s BioNet database (https://programs.iowadnr.gov/bionet/). The results from this follow-up sampling and comparison of these results to ecoregion averages suggested that the fish community of this stream segment in 2011 was similar to or better than non-fishkill impacted streams. Although the results of the fishkill follow-up sampling lack the scientific rigor to determine whether the designated aquatic life uses are “fully supported,” the results indicated that the stream had recovered from the September 2003 fish kill event upon which the impairment of aquatic life uses was based. Thus, for the 2012 IR cycle, this stream segment was moved from impairment Category 5b of Iowa’s Integrated Report to Category 3a (designated use not assessed). The presumptive Class B(WW1) aquatic life uses remain in Category 3a of the Integrated Report.
