Secchi Disk

Turn how clear a lake looks into a number you can track

The Secchi Disk is an 8.75" white plastic disk marked with black and white quadrants, attached to a weighted, foot-marked line. Lower it into a lake, pond, stream, or aquarium until the pattern disappears from view, then read the depth off the line. That depth, the Secchi depth, is a standard field measurement of water clarity used by limnologists and water quality monitoring programs.

The disk's pattern is permanently screen-printed, so it won't scratch or fade off after repeated dunkings. The line is rot-proof polymer wound on a foam bobbin, marked at every foot, and an attached sinker keeps the disk dropping straight down instead of drifting in current. No meter, batteries, or calibration involved, just a disk, a line, and a clear reading each time.

Works for pond, lake, and stream water quality studies, environmental science and limnology units, and citizen science water monitoring programs, from middle school through college.

Why Teachers Love It

• One Reading, One Number – The disappearance depth requires no equipment or calibration, just a value students can log and compare across sites or visits.

• Track Water Clarity Over Time – Students can survey the same pond or stream across a semester, turning Secchi depth into a real, ongoing dataset instead of a one-time measurement.

• Field-Ready Durability – Permanent screen-printed pattern and rot-proof line hold up to repeated trips into the water.