Streamwater samples were collected at 19 sites in the vicinity of the Oneida Tribe of Indians of Wisconsin Reservation. Samples were collected during 5 sampling periods in 1997-98. Field measurements were made and samples were analyzed for nutrients, suspended sediment, major ions, and pesticides.

Physical characteristics and human activity influence surface-water quality in the study area. Predominant land use in a drainage basin, specifically agricultural land use, appears to be a strong influence on surface-water quality. Other important influences on surface-water quality in the Oneida Reservation area include point-source contamination, size of the drainage basin, presence of clayey surficial deposits, and the timing and flow conditions during sampling.

Concentrations of total phosphorus and of dissolved nitrite plus nitrate nitrogen often exceeded U.S. Environmental Protection Agency (USEPA) Maximum Contaminant Levels (MCL's). Concentrations of nutrients were highest at sites with greater than 80 percent agricultural land use in the drainage basin.

Sodium and manganese were the major ions that most often exceeded USEPA water-quality criteria. The highest concentrations of sodium and chloride were detected at three sites in basins containing greater than 10 percent urban land and at two of ten sites in basins containing greater than 80 percent agricultural land.

Concentrations of the pesticides atrazine, cyanazine, and diazinon exceeded MCL's at several sites. Elevated concentrations of agricultural pesticides were detected primarily at sites in basins containing greater than 80 percent agricultural land, in comparison to pesticide concentrations at sites in basins containing lesser amounts of agricultural land. Diazinon concentrations were higher at sites in basins containing more than 10 percent urban land compared to basins with little to no urban land.

Stream habitat at three sites was rated "good" on the basis of the semiquantitative Great Lakes Environment Assessment procedure. On the basis of the semiquantitative procedure, habitat at three other sites was impaired, likely because of agricultural influences and tendencies towards low flow in the summer.

Assessments of benthic community health based on benthic invertebrates showed that the communities were "very good" at one site, "good" at three sites, "fair" at one site, and "fairly poor" at one site. Mean tolerance values yielded similar assessments of the invertebrate communities. Taxa richness for pollution-sensitive insect orders indicates that water-quality is best at Thornberry Creek. Water-quality at Trout Creek and Lancaster Brook also rated fairly high. Shannon-Wiener diversity values indicate that the invertebrate communities at Dutchman Creek, and perhaps at Duck and Oneida Creeks, are under environmental stress.

Assessments of the benthic algal community provided relative results as did invertebrate community assessments. Shannon-Wiener diversity values for diatoms indicate that algal communities are under minor stress in four of five streams sampled and under moderate stress in Dutchman Creek. A pollution index based on the percentages of diatoms that are pollution sensitive and pollution tolerant revealed that pollution at Dutchman Creek likely is moderate; pollution at the other four sampled creeks is either minor or nonexistent in terms of effects on the diatom community.