North River IA 04-LDM-1097

Assessment Comments

Assessment is based on (1) results of DNR monthly monitoring SE of Norwalk in 2000-01 and (2) 1998 DNR/UHL biocriteria sampling (Fish IBI= 11(poor), BM-IBI= 60(good)).

Basis for Assessment

SUMMARY:  The Class B(WW) aquatic life remain assessed as "partially supported."  Fish consumption uses are "not assessed."  The sources of data for this assessment include (1) results of biological (biocriteria) monitoring in 1998 and (2) results of IDNR ambient monthly monitoring during the 2000-2001 biennial period at station 10910002 (formerly station 426058) at the County Road R27 bridge SE of Norwalk.   EXPLANATION:  The Class B(WW) aquatic life uses were assessed based on the 1998 biological assessment data [the recalculated Fish IBI score = 11 (poor),BM-IBI score = 60 (good)], and the aquatic life use support continued to be 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.  

Despite the results of biological monitoring that show impairment, results of chemical monitoring in this river segment continue to show relatively good water quality.   None of the 24 samples collected during the 2000-2001 biennial period at the IDNR monthly ambient station violated Class B(WW) water quality criteria for pH, dissolved oxygen, or ammonia-nitrogen; no violations occurred in the four samples analyzed for toxic metals or in the six samples analyzed for pesticides and other toxic organic compounds.   Fish consumption uses are "not assessed" due to the lack of recent fish contaminant monitoring in this stream segment.