This discussion is about 0.7 ppm fluoride ion in drinking water not industrial pollution events.   High concentration of fluoride in the Columbia River could interfere with Salmon Migration, but the addition of 0.7 ppm to drinking water causes no measurable change in stream fluoride because it is an inconsequential amount.    

Talking about industrial pollution levels of fluoride is a common propaganda theme of water fluoridation opponents. . the two matters are practically unrelated.