Floyd River IA 06-FLO-1554

Assessment Comments

Assessment is based on occurrence of fish kills in May 1997 and September 1998 and 1995 Biocriteria sampling in O'Brien county: FIBI = 36 (fair) and BMIBI = 68 (good).

Basis for Assessment

The Class B(LR) aquatic life uses were assessed as "not supported.   A fish kill occurred on the Floyd River at, and 15 miles downstream from, Sheldon in Sioux County on September 24, 1998.   Contents of a catchment basin surrounding a tank with 28% nitrogen were pumped into a storm sewer following a rainfall event.   Toxic materials were discharged from the storm sewer to a drainage way one-quarter mile from the Floyd River.   An estimated 408,000 fish were killed over the 15 mile reach affected by the kill.   Due to the occurrence of two kills in the 1994-99 assessment period, the Class B(LR) aquatic life uses of this river reach were assessed as PS.  No additional information exists for assessing the water quality of this waterbody segment.   Restitution for both kills was requested and received by DNR (1997 kill:  Northwest Iowa Cooperative; 1998 kill:  Midwest Farmer's Cooperative).   The occurrence of this kill, and an additional fish kill at Sheldon in May 1997 (see assessment for the 1998 report above) suggests that the Class B(LR) aquatic life uses are "not supported."  According to DNR's assessment methodology for Section 305(b) reporting, occurrence of two or more pollution-caused kills within the most recent three-year period (1997-1999) indicates that the aquatic life uses are "not supported."  Thus, the assessment of support of the Class B(LR) aquatic life uses for this stream reach were changed from "fully supported / threatened" to "not supported" due to reoccurring fish kills.

The 1995 DNR/UHL biocriteria sampling site was located upstream from the fish kill affected stream segment approximately 1 mile north of Sheldon.   A series of biological metrics which reflect stream water quality and habitat integrity were calculated from the biocriteria sampling data.   The biological metrics are based on the numbers and types of benthic macroinvertebrate taxa and fish species that were collected in the stream sampling reach.    The biological metrics were combined to make a fish community index of biotic integrity (F-IBI) and a benthic macroinvertebrate index (BM-IBI).   The indexes rank the biological integrity of a stream sampling reach on a rising scale from 0 (minimum)-100 (maximum).   The F-IBI score was 36 (fair), and the BM-IBI score was 68 (good).   The aquatic life use support status for this sampling reach of stream was assessed as fully supporting / threatened (=FS/T), based on a comparison of the F-IBI and BM-IBI scores with biological assessment criteria established specifically for the 2000 Section 305b report (IDNR 2000).   The biological assessment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-1998.  

The final use support determination was primarily based on the more recent reports (1997, 1998) of fish kills which affected a larger proportion of the stream segment than was represented by the 1995 biocriteria sampling site.   The biocriteria sampling results of 1995 indicate the stream can attain full support of aquatic life uses if pollution impacts can be prevented.