Book 30, Question 109
What does a Secchi disk reading tell you about a lake’s health?
A Secchi reading is a quick measure of how clear a lake is.
A shallow reading, where the disk vanishes just below the surface, means the water holds lots of algae or mud. A deep reading means the water is clear. Over many years, readings can show whether a lake is getting greener. In Ontario, volunteers take Secchi readings through a lake program so scientists can track changes across many lakes.
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Quick answers
What does a Secchi disk reading tell you about a lake’s health?
Secchi disks are a water clarity measurement tool that indicates how clear lakes are by observing how deep an 8-inch white disk on a line can be lowered into the water.
Source: University of Minnesota
More fun facts
- Water clarity is an important measurement of lake condition.
- Lower the disk slowly into the water with the black and white side facing up.
- The depth at which the disk is no longer visible is recorded as the Secchi depth transparency.
- The Secchi depth reading is the average between the two noted readings.
- Lean over the shady side of the boat and slowly lower the Secchi disk into the water until it can no longer be seen.
Sources: apps.dnr.wi.gov, University of Minnesota, Indiana