Secchi Tube Classroom Activity

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Resource Types: 

This classroom activity or student project includes instructions on how to conduct a lesson that uses the Secchi tube to measure and compare stream transparency from collected water samples. Included in the lesson are equipment needs, ideas for water sampling locations, instructions for a long-term project and a one-time project, and more.

The Secchi-tube is a modified transparency tube that is designed to function like the traditional Secchi disk used in lake monitoring. To measure water clarity, the tube is filled with water collected from a stream or river. Looking down into the tube, a weighted Secchi disk is lowered into the tube by a line, allowing the user to raise and lower the disk within the same water sample numerous times.

Tracking water transparency is like monitoring your blood pressure because it tells us about the health of a stream. Changes in transparency tell us when key water pollutants are present. In general, a low transparency reading reflects a large amount of sediment (excessive soil material) or other suspended material like algae in the water. Too much sediment in the water is a significant pollutant itself, whether it is suspended in the water column or deposited on stream bottoms.

For more information about secchi tubes visit

The classroom activity can be found at

Topic Areas: 
Outdoor Education
Natural Sciences
Target Audience: 
Grades Pre K-12
Citizen and Youth Groups
Geographic Location: 
All Minnesota
Library loan: 
Is training required?: 
Contact(s) or order information.: 

Minnesota Pollution Control Agency
Learning Resource Center & Library
520 Lafayette Rd N
Saint Paul, MN 55155-4194