The most common effects on fish observed during this study have been tearing of the gill covers and loss of scales. Findings from this study could provide hydroelectric dam operators with some of the information necessary to design fish-friendly turbines. To simulate the environment found within a turbine channel, Pacific Northwest researchers built a small-scale facility that uses an underwater jet nozzle to vary water velocity. Researchers have begun testing the impact to fish of velocities ranging from zero feet per second to 60 feet per second. They will identify the injury threshold - the points at which there are no, or few, injuries to fish.
Turbines are integral to the operation of hydroelectric dams, but they also can injure fish.
Turbine passage can be considered one of the more fatal routes that fish take through hydroelectric dams. Mortality rates range from 4 to 20 percent, depending on factors such as type of turbine and type of fish. During passage through a dam, a fish experiences several changes in water velocity and encounters shear forces during each velocity change. The most intense shear forces usually exist near the turbine blades and, most especially, the tips of the blades. In field tests at Pacific Northwest's aquatic facility, researchers introduce fish individually through a tube above a water nozzle.