Do you know where your local stream, creek or river rises? Why not?
Is there any point in cleaning a river downstream if pollution is pouring in to it further upstream.
Water ways need to be looked at as part of an entire catchment above and below ground as polluted ground water can be deadly as soon as it reaches the surface.
Water flows downhill so water inland will wind its way to the ocean along with anything that floats. in the 21st Century the biggest issues is floating plastic: Cigarette butts, plastic bottles, plastic bags, food packaging...