Some people are poised to assume it's good etiquette to use water ways as latrines. I've pissed in a creek before, but it's better to do your business away from water ways as it allows for the transmission of water borne illnesses such as hepatitis, cholera, dysentery, and polio. Reason you have to boil water that comes from streams and creeks with aquatic organisms is because there's potential parasite eggs, and protozoans which use humans as hosts. Depends as well on the river, you can shit in the major water ways of the united states, except ones that empty into the great lakes. If it's sourced from a spring though, due to local hydrology, best to use it as a water source and respect it.