I assessed the quality of salmonid hatchery effluents and receiving streams in Washington State during the 1988 summer low-flow period. Relative to hatchery influent waters, effluents showed significant increases in temperature, pH, suspended solids, ammonia, organic nitrogen, total phosphorus, and chemical oxygen demand. Wastewater discharges sometimes violated state water quality standards; effects were exacerbated by low dilution. Hatchery nutrient loads equalled or exceeded receiving water loads; effects of enrichment were most evident in oligotrophic waters. Benthic invertebrates sensitive to organic waste were often replaced by pollution-tolerant forms in the vicinity of hatchery outfalls. Survey findings necessitated revision of existing hatchery wastewater discharge permits in Washington.