Poisons are deadly to many fish, crustaceans, and especially the small aquatic insects that are the primary food source for the aquatic ecosystem.
They are sensitive to poisons because they breathe from water, and the poisons enter the blood system directly through their gills.
Poisons take at least 8 days to decompose, and they do a lot of damage all the way down the river during this active time. This not only affects the site of use.
The effects of ingesting poison range from blindness to seizures, diarrhea and skin infections.