Secchi Disk—Water Quality Test

Scientific Concepts / Nature Phenomena

• Secchi disk water-quality test (Secchi depth / light penetration):
  • A Secchi disk is lowered into water to determine how far down it remains visible.
  • The procedure involves lowering and raising the disk while observing when it is no longer clearly seen.
  • The depth at which the disk becomes barely visible is used as a measure related to water clarity, which can be influenced by factors such as suspended particles and turbidity.

Methodology (as described)

1. Attach/prepare the Secchi disk:
   • Tie or secure the disk to a line.
2. Lower the disk into the water.
3. Observe visibility while lowering:
   • Hold the disk up to confirm it is clear and visible (including when visible at greater depth, as described).
4. Raise the disk until it is barely visible.
5. Record the Secchi depth:
   • The example depth mentioned is 123 meters (when the disk becomes “barely seen”).

Featured Researchers / Sources

• None mentioned.