A field sampling program was conducted during the spring-summer of 1985 and 1986 at a test facility located offshore of Ontario Hydro's Pickering Nuclear Generating Station (NGS) on Lake Ontario. The objective of the field program was to evaluate the effectiveness of selected behavioral barriers for fish exclusion at generating facilities located on large freshwater lakes or impoundments. Three commercially available devices (air bubble curtain, pneumatic gun, and underwater strobe lights) were tested alone and in combination to determine their effectiveness in reducing impingement. Sampling was conducted at two identical structures with the behavioral barrier devices installed on one of the structures and the other structure acting as a control. The effectiveness of the devices at excluding alewife (the dominant local species) was determined by comparing net catches covering 2-h test periods between the two structures. All of the behavioral barrier devices or combinations of devices tested exhibited effectiveness index values greater than 50%. The greatest deterrent capability was associated with the pneumatic gun; the least with the air bubble curtain. Device combinations that included the pneumatic gun were generally less effective than the pneumatic gun alone. The underwater strobe light was only marginally effective at excluding alewife. The air bubble curtain and underwater strobe light combination was more effective than each device separately, but the results were variable. This field testing was the first of two sites in a multi-year study cosponsored by the Electric Power Research Institute (EPRI) and a group of cofunding utilities. http://www.epri.com