Assessment Comments
Assessment is based on (1) occurrence of fish kill in August 1998 (see attached document for details) and (2) 2000 Biocriteria: Fish IBI= 36(fair), 66(good); BM-IBI= 45,(fair),62(good).
Basis for Assessment
[Note: For the 2002 report, the previous waterbody segment for the Indian Creek (IA 02-CED-0210-0), which extended 16 miles from its mouth to an unnamed tributary in Linn County, was split into two subsegments: (1) mouth to Dry Creek (IA 02-CED-0210-1) and (2) Dry Creek to unnamed tributary in S20, T84N, R6W, Linn Co, approximately 2 miles NNE of Marion (IA 02-CED-0210-2). See above for previous Section 305(b) assessments for the original 16-mile river reach.]
The Class B(LR) aquatic life uses continued to be assessed as "partially supported" based on the occurrence of the 1998 fishkill (see 2000 assessment comments), and biological sampling data collected in 2000 as part of the DNR/UHL stream biocriteria 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) to 100 (maximum). The 2000 Fish IBI scores were 36 (fair) and 66 (good); the BM-IBI scores were 45 (fair) and 62 (good). The aquatic life use support was assessed as partially supporting (=PS), based on a comparison of the F-IBI and BM-IBI scores with biological assessment criteria established specifically for the 2002 Section 305(b) report. The biological assessment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2001.
