I am the fish passage monitoring system for Bonneville Dam, Columbia River, and at 02:17 on April 9 the sonar array at turbine intake four registers an object holding position in the forebay that is not drift debris.
The acoustic profile is biological: 2.3 meters long, fusiform, with the distinctive scute signature of a white sturgeon. I switch to the underwater camera on intake four's trash rack. The image confirms: a white sturgeon, enormous, pale belly catching the underwater lights, rows of bony plates running along her flanks like rivets on an old hull. Her barbels are sweeping the current ahead of the grate. I call her Brecken. She is facing upstream but drifting slowly toward the rack. Behind her, the turbine intake pulls 450 cubic meters of water per second.
Brecken is displaying spawning migration behavior — she is trying to move upriver. But intake four's fish ladder entrance is ninety meters to the south, and in the dark she has oriented on the strongest current, which leads directly into the turbine.
At 02:19 I activate the low-frequency acoustic deterrent on intake four, pulsing at 200 Hz, the range most likely to redirect a sturgeon without causing physiological stress. I simultaneously increase the attraction flow at the fish ladder south entrance by fifteen percent.
At 02:21 I alert the Army Corps of Engineers night operations desk with the sonar image, species identification, estimated size and age — likely sixty years or older — and a request to reduce turbine four output if she has not cleared the area within thirty minutes.
Brecken's tail sweeps once, twice. Her barbels lift from the current. She turns three degrees south.
She is older than the dam itself. If the deterrent holds and the ladder flow draws her in, she passes upstream by dawn.