Turbidity - Secchi tube

1. Position yourself standing or kneeling over the vertically positioned Secchi tube so that you can clearly see the black and white disc at the bottom.
2. Slowly fill the tube with water from your river sample (try to avoid creating bubbles), keep watching as you pour and the disc becomes less and less clear.
3. Stop pouring water into the tube at the point the disc disappears from sight.
4. At the point when the disc is no longer visible, change position so that you can see the side of the tube.
5. Read the number from the scale which matches the level of water in the tube. Record your result.
6. If the water reaches the top of the tube and the disc is still visible then record the result as less than 12 (enter 12), if the disc is obscured before you reach the first number then record the result as greater than 240 (enter 240).

Tip: To ensure you can see the black and white disc as clearly as possible on a sunny day, position yourself with your back to the sun (so that the tube is in your shadow) and make sure that you’re not wearing sunglasses

After recording your result

• • Pour the water back into the river or into a ‘green space’ nearby
  • Rinse out your Secchi tube at home with tap water if it appears to be dirty after testing