Assessment Comments

Assessment is based on (1) 2002 IDNR biocriteria sampling data and (2) occurrence of a fish kill in July 2002.

Basis for Assessment

SUMMARY:  The Class B(CW) aquatic life uses remain assessed (monitored) as "not supported" based on results of biological monitoring in 2002 conducted as part of the IDNR/UHL stream biocriteria project.   Occurrence of a fish kill, possibly caused by runoff by land-applied manure, suggests an additional impairment of the aquatic life uses.   Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this stream reach.  

EXPLANATION:  The assessment of the Class B(CW) aquatic life uses was based on data collected in 2002 as part of the DNR/UHL stream biocriteria project.   A series of eight (8) coldwater biological indicators, which reflect stream water quality and habitat integrity, were calculated from the biocriteria sampling data and supplemental IDNR Fisheries Bureau data.   The coldwater biological indicators are based on the numbers and types of coldwater benthic macroinvertebrate taxa and fish species that were collected in the stream sampling reach.   Sites that score 7 or 8 are Fully Supporting (FS), sites that score 4-6 are Fully Supporting/Threatened (FS/T), sites that score 2-3 are Partially Supporting (PS), and sites that score 0-1 are Not Supporting (NS).   The 2002 coldwater biological indicator score was 0/8.   The aquatic life use support was assessed as Not Supporting (=NS), based on a comparison of the coldwater biological indicator score with biological assessment criteria established for this Section 305(b) report.   The coldwater biological indicators were determined from a statistical analysis of data collected at coldwater stream ecoregion reference sites from 1994-2002 and with assistance from the IDNR Fisheries Bureau.  

Physical habitat assessment was conducted and a water quality sample was collected on the August 13, 2002 biological sampling date.   An elevated level of silt substrate was observed and a beaver dam was observed immediately upstream from the sample site.   Ammonia-nitrogen (0.32 mg/L) and total phosphorus (0.32) levels were elevated during low stream flow.   The dissolved oxygen level (4.4 mg/L) was lower than expected for daytime.

In addition, a fish kill occurred on this stream on July 29, 2002.   The kill followed heavy rainfall following a long period of hot, dry weather.   No specific cause was determined, but runoff from feedlots and/or land applied manure is suspected due to presence of several feedlots in the watershed of this stream.   Approximately 0.5 mile of stream was affected, and 184 fish were killed.   According to IDNR's assessment methodology for Section 305(b) reporting, occurrence of a single pollution-caused fish kill within the most recent three-year period indicates ongoing impairment of the aquatic life uses.  

Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this stream segment.