How to Find the Secchi Depth

The Secchi disk reading is a measurement of water clarity.

One of the most common ways to determine water clarity is via a Secchi disk reading. A Secchi disk is a circular disk that is all white, or black and white. The disk is lowered into the water by means of a cord attached to its center. The cord is marked in 6- and 12-inch intervals, which aid in determining depth. The Secchi depth is the depth at which the Secchi disk disappears from view.

Things You'll Need

• Secchi disk
• Boat

Instructions

1. Drive the boat to the spot where you want to check the Secchi depth.

2. Position the boat so one side is shaded.

3. Lower the Secchi disk into the water on the shaded side of the boat. Continue lowering it until it disappears from view. Check the cord to see the depth.

4. Pull the disk up until you can see it. Check the cord to see the depth.

5. Add the two depth readings and divide them by two to determine the Secchi depth.

References

• RMB Environmental Laboratories: How to Use a Secchi Disk