Detailed project planning for cleaning an urban river system in Zimbabwe.

I am a solar pump engineer with a very basic understanding (from a long forgotten university course) on how to test for river water quality, how should the samples be collected etc.  I have been contacted by a community of urban farmers who want to clean their local water source in Harare. I need your professional help in this regard. Question one - Can we do river restoration or river cleaning at selected river section?  Question two - what should be the detailed process for the "Sectional River Cleaning" project ? I'd be extremely grateful to river restoration professionals for giving me inputs on methodology, reference sites, hints, or tips on this topic.