Coastal marine environments are commonly used for disposal of industrial waste, dredge spoils and sewage sludge, which contain high concentrations of copper and other heavy metals. For example, in the New York Bight, a daily input of copper at 14 tons is estimated. This input has resulted in concentrations up to 390 mg kg/sup -1/ (dry) Cu in the sediment and concentrations as high as 20 ..mu..g L/sup -1/ in the seawater. Adverse effects of copper on some species of marine life have been well documented. However, most toxicity data available for bivalves are from static acute toxicity tests, even though long-term flowing water bioassays provide more realistic exposure conditions. To date, no studies have been conducted on copper toxicity to the bay scallop, Argopecten irradians, a commercially important species. The purpose of this study was to examine the effect of copper on survival, growth, and byssal attachment, and copper accumulation of juvenile bay scallops in a flowing water exposure system.