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CHRISTOPHER M. KAVANAUGH 15 Table 5. Macroinvertebrate richness, diversity, and biotic integrity (MBI) at 19 mainstem and tributary sites sampled in 1989-90. Richness Diversity MBI Station 1989 1990 1989 1990 1989 1990 Mainstem Henderson 15 19 1.77 1.54 5.27 7.69 St. Peter 24 24 2.32 3.~ 4.93 5.05 Judson 34a 23 2.60 3.00- 5.92 5.45 Cowtland 27a 24 2.61 2.82 5.33 5.55 Folt Ridgely 2sa 23 2.21 1.47 5.11 4.37 Morton 3~ 22 2.38 2.84 4.62 5.59 Delhi 2'f1 23 2.85 2.76 5.26 4.87 Upper Sioux 23 2'f1 1.63 2.17 7.93 7.21 Lac Qui Parle 12 22 2.47 1.11 5.54 3.56 Tributary High Island Creek 21 17 2.78 2.62 4.62 4.67 Rush River 31a 19 4.10- 2.65 6.59 6.39 Blue Earth River 21 18 3.ocr 3.35a 6.37 5.26 Le Sueur River 35a 22 3.54a 3.1g& 5.23 3.84 Watonwan River <Jd 31a 3.67a 4.04a 5.97 6.17 Cottonwood River 25 22 2.46 3.05a 7.91 4.76 Redwood River <Jd 2()'1 3.00a 3.33a 5.88 5.69 Hawk Creek 24 22 3.17a 2.29 6.64 5.42 Yellow Med. Riv. 19 21 2.41 2.74 4.37 4.67 Chippewa River 17 19 2.40 2.00 6.85 8.46 aConsidered affected. Fish samples were taken from two tributary (Cottonwood. and Blue Earth rivers) and two main- stem sites. Species collected included common carp, smallmouth bass, and sauger. Liver microso- mal aminopyrine N-demethylase activities were measured, and the PCB analysis is ongoing. Liver microsomal aminopyrine N-demethylase activity was higher at the Judson site (mainstem) than at all other sites in 1989. In 1990, liver en- zyme activities in common carp samples were higher at the Cottonwood River site and lower at the Judson site. Additional fish were collected in 1992 to test the hypothesis of high pollutant concentrations in low- flow years in the Minnesota. River and high-flow years in the tributaries. Fish Community The Minnesota. River basin provides an impor- tant fishery resource for southern Minnesota.. Channel catfish, flathead catfish, walleye, sauger, and northern pike support most of the sport fishery in the streams of the basin. A commercial fishery exists for common carp, buffalo, and freshwater drum. Comprehensive fisheries assessments through- out the basin are lacking. Kirsch et al. (1985) sur- veyed the mainstem Minnesota. River from 1980 to 1982. The Minnesota. Department of Natural Re- sources has assessed segments of the mainstem and some major tributaries. However, there has never been a comprehensive assessment of fish communities throughout the basin. The index of biotic integrity (lB1) is an ecologi- cally based index used to assess degradation in midwestem streams (Karr 1981). The method has been modified to assess degradation of streams in a variety of ecoregions throughout North America (Leonard and Orth 1986; Hughes and Gammon 1987; Ohio Environmental Protection Agency 1987; Miller et al. 1988; Steedman 1988; Fausch et al. 1990; Bramblett and Fausch 1991). The regional fish fauna was examined by a team of Minnesota. Department of Natural Resources and MPCA staff and ichthyologists from the Uni- versity of Minnesota. (Professors J. Underhill and J. Hatch). This team reviewed and evaluated the metrics proposed by Karr (1981), Fausch et al. (1984), and Karr et al. (1986) and their underlying rationale. The team developed replacement met- rics or rationale where necessary to confonn with