Sensor Fish data shows rapid pressure drop kills salmon at Columbia River dams

August 24, 2026 at 06:48 AM2 min

This digest was compiled by AI from multiple sources — links to the originals are below.

Engineers at Pacific Northwest National Laboratory used robotic Sensor Fish to record pressure changes inside Columbia River dam turbines. Lab tests on 5,767 juvenile Chinook salmon showed rapid decompression alone causes injuries seen in turbine-passed fish. The study published in Transactions of the American Fisheries Society identifies pressure ratio as the best predictor of death.

Key Facts

Sensor Fish recorded pressure plunging from deep-water levels to below atmospheric pressure in seconds near turbine runner blades.
5,767 juvenile Chinook salmon were tested in hyperbaric chambers with nadirs as low as 4.8 kilopascals.
The study published in Transactions of the American Fisheries Society found pressure ratio best predicted death.
Most dead turbine-passed smolts showed no external injuries, suggesting a non-contact cause.

Sensor Fish Deployment

Pacific Northwest National Laboratory engineers built the Sensor Fish, a rugged cylinder about the size of a smolt, packed with instruments recording pressure, acceleration, rotation, and temperature 2,000 times a second. Researchers released the devices into dam intakes on the Columbia River, including runs at Ice Harbor, John Day, and Bonneville. The recorded pressure profiles showed catastrophic drops near runner blades, with worst passages going from deep-water squeeze to well below atmospheric pressure almost instantly. Fisheries scientists compared the worst-case exposure to traveling from the bottom of a swimming pool's deep end to the top of Mount Everest in a blink.

Laboratory Pressure Tests

PNNL fish physiologist Richard Brown led a team that rebuilt the turbine ride in hyperbaric chambers, acclimating juvenile Chinook salmon to river-depth pressures before applying rapid decompression. Across the research program, 5,767 juvenile Chinook salmon were run through simulated turbine pressure regimes with nadirs as low as 4.8 kilopascals, about a twentieth of atmospheric pressure. Pressure alone reproduced the injuries found in turbine-passed fish, settling the question of non-contact mortality. The study published in Transactions of the American Fisheries Society found the ratio between acclimation pressure and lowest pressure hit was the single best predictor of death.

Injury Mechanism

A salmon's swim bladder is a gas-filled sac used for buoyancy control, and Boyle's Law states gas volume balloons as pressure falls. The rapid decompression targets the swim bladder, causing internal injuries without external scratches. The deeper the fish had been living and the lower the pressure trough behind the blade, the worse its odds of survival.