How do you check how good a rivers quality is?

Question: How do you check how good a rivers quality is?
- Keywords:
  pollution,
  river,
  water,
  work
Asked by Thomasthetankengine to Karen on 16 Nov 2018.
- Karen answered on 16 Nov 2018:
  
  I use something called a turbidity sonde which is a machine that shoots out a small beam of light into the water, and measures the amount of light that hits the dirt (soil) and bounces back 🙂

Question: How do you check how good a rivers quality is?