A critical examination of an aquatic environment adjacent to the discharge from an unbleached kraft pulp and paper mill (UBKM) was conducted in 1995. The assessment involved sampling of sediments, water, benthic macroinvertebrates, and fish collected 1.6 km upstream from the mill, at the mill's outlet, and 2.5 km downstream. Field-collected blue catfish (Ictalurus furcatus) and bluegill sunfish (Lepomis macrochisus) exposed to site sediments in the laboratory showed no significant within-organism adverse effects as measured by EROD activity, benzo[a]pyrene hydroxylase activity, CYP1A content, DNA damage, condition factor, organ indices, differential blood cell counts, and histopathology, though DNA strand breaks increased at the most downstream site. No aqueous or sediment toxicity was observed using Ceriodapnia dubia and Pimephales promelas or Hyalella azteca and Chironomus tentans, respectively. Embryos of the mosquitofish (Gambusia affinis) were evaluated for reproductive potential following laboratory exposures of adult mosquitofish to river sediments and water for 90 days. No significant adverse reproductive effects were observed immediately below the BKME discharge site. Analyses of field-collected benthic macroinvertebrate samples revealed no significant effects in terms of taxa, taxa richness, and other measures of their status. Using a comprehensive suite of within-organism, whole-organism, and community level endpoints, our study demonstrates that this effluent, discharged following secondary treatment from an UBKM, had no significant adverse impacts on the receiving aquatic ecosystem.