Creeks and small rivers are sometimes diverted in cities or sometimes even covered over. Cities historically have polluted the waterways they are on, but that is becoming less as more people become aware that waterways are not dumps. But the larger the city, the more impact it will have on its creeks and rivers. Sewer drains always carry junk that will pollute a river. Rapid runoff because of no vegetation cover of the soil also affects rivers.
