
But the water, even its extremely polluted, still looks like this:

With sewage in the river the water should be dark.
So this is my suggestion: DARKER lakes/rivers/oceans and BLACK GRASS in lands at sewage pollution.
Also it can pollute water producers (Water tower, water pumps, etc.) Constructing water producing buildings in a land that is polluted with sewage can cause health problems and unclean water.