Kgabo -- I agree with James ...

Kgabo -- I agree with James and Maria in approach to point and non-point pollution sources. Additionally, sometimes a river's floodplain has ox-bows (old river paths) which can be regraded and reintroduced as naturally revegetated wetland pathways. This allows for pathogen treatment and biodiversity support. I do not know where this has been done (at scale); a good start was made in the US Des Plaines River in the 1980s - there's much current internet info on it. (Your E. coli levels are particularly high and indicate a 'point source' -- like a city...) Best wishes!