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The Secchi Disk

The Secchi disk is a tool used to measure the clarity of water. It is a circular plate, usually divided into 4 alternating quadrants of black and white. The diameter is typically 20 centimeters (roughly 8 inches).

The Secchi disk is lowered by a rope into the water until it is no longer visible. The rope is marked at the surface of the water with a clothespin. The Secchi disk is then lowered a couple of feet deeper into the lake and slowly brought back up until the disk is visible. The rope is again marked with a clothespin at the surface of the water. The distance from the Secchi to each clothespin is measured and the average of the two is the Secchi transparency readings.

The Secchi disk in use

Secchi is used to quanitfy clarity

Secchi illustration

In clear water, the Secchi disk will be visible at a greater depth than in murky water.

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The Lakes of Missouri Volunteer Program is operated by employees of the University of Missouri