North River IA 04-LDM-1097

Assessment Comments

Assessment is based on results of DNR monthly monitoring SE of Norwalk.

Basis for Assessment

SUMMARY:  Assessed support of the Class B(WW) aquatic life uses as "partially supported."  Fish consumption uses were "not assessed."  EXPLANATION:  Results of the DNR stream assessment conducted in September 1990-upon which the previous assessment of the Class B(WW) uses was primarily based-are now considered too old (greater than five years) to be useful for assessing current water quality conditions.   Thus, the assessment of the Class B(WW) uses was based on (1) results of monthly chemical monitoring at the Norwalk station during the 1998-1999 biennial period and (2) a 1998 sampling of fish and benthic macroinvertebrates as part of the DNR/UHL biocriteria project.   Results of DNR monthly (chemical) monitoring showed no violations of Class B(WW) (aquatic life) water quality criteria in the 24 samples analyzed for dissolved oxygen, pH, and ammonia, and in the two samples analyzed for toxic metals.   Despite the apparently good chemical water quality, results of biological sampling suggest an impairment of the aquatic life uses.   Based on results of regional reference site sampling, the fish community was rated "poor" (fish IBI=20) while the benthic macroinvertebrate community was rated "good" (BM IBI=60).   Based on the relatively poor-quality fish community, the Class B(WW) aquatic life uses were assessed as "partially supported."  Fish consumption uses were not assessed due to lack of fish tissue monitoring in this river reach.