Pennsylvania Fish and Boat Commission periodically does electrofishing in the Letort Spring Run to survey the fish population. Biologists wade in the stream, one wearing wears a backpack that has a control box and either a generator or a battery pack.
Others hold electrodes that transmit electricity to the water. Fish near the electrodes are attracted like a paper clip to a magnet, and others are temporarily stunned. The biologists net the fish and identify, count and measure them. The fish are released unharmed.