Willow Creek IA 06-LSR-1611

Assessment Comments

Assessment based on results of a 1995 Biocriteria sampling conducted in Cherokee county.

Basis for Assessment

The DNR/EPD stream assessment project data collected in 1989 were not used to determine the degree of aquatic life use support for this waterbody segment because the data are more than five years old, and no longer considered current.   The assessment was based on data collected in 1995 as part of the DNR/UHL stream biocriteria development project.   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 40(fair), and the BM-IBI score was 46(fair).   The aquatic life use support status 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.   Physical habitat was rated as fairly-good in the reach of stream sampled.   Livestock grazing impacts in the stream riparian zone and channel modifications caused by historic stream channelization projects probably pose the greatest threat to the stream's biological community.