For decades, coho salmon returning from the Pacific Ocean to the creeks and streams of Puget Sound in Washington state to spawn were dying in large numbers. No one knew why. Scientists working to solve the mystery of the mass deaths noticed they occurred after heavy rains.
Toxicologists suspected pesticides, as the main creek they studied ran through a golf course. But no evidence of pesticides was found. They ruled out disease, lack of oxygen and chemicals such as metals and hydrocarbons.
