Parish or town council
Residents email you every time the river looks wrong, and you have no figures to answer with.
River Truth gives the council a page for your own stretch: every spill from the overflows near you, how long it ran, the rain beforehand, and the Environment Agency's own sample results. When a resident asks, you send the link. When you write to the water company, you quote their own data back to them.
Fits: Council or Larger council