When there is fluoride in river water at low levels, salmon swim the other way.

See these journal articles:

Salmon – repelled by fluoridation at only .25 ppm, Columbia River, Washington, Frasier River, Kamloops, British Columbia, summary of peer reviewed journal articles.

Salmon – Foulkes & Anderson, Impact of Artificial Fluoridation on Salmon Species in the Northwest USA and British Columbia, Canada, Fluoride, Vol 27, No 4, 220-226 (1994.)

Colorful_Fish

Snohomish River Salmon Run Crashes – Fluoridation Connection