Quick Answer:The Secchi Disk measures water clarity: a 7.7" white plastic disk with screen-printed black sectors, an attached sinker and a rot-proof polymer line of approximately 72 ft (22 m), marked at each foot, on a foam bobbin.
Last updated: 18 October 2026
Key Features
White plastic disk, 7.7" in diameter, with permanent screen-printed black sectors.
Attached sinker takes the disk down through the water.
Rot-proof polymer line, approximately 72 ft (22 m) long.
Line marked at every foot for reading depth.
Line stored on a polymer foam bobbin.
Technical Specifications
Specification
Value
Disk
White plastic, permanent screen-printed black sectors
Disk diameter
7.7"
Line
Rot-proof polymer, approx. 72 ft (22 m)
Line markings
Every foot
Sinker
Attached
Bobbin
Polymer foam
Packed weight
1.5 lb
Packed size
8.75" diameter x 2" height
How It Is Used
The disk is lowered on its line into a pond, lake or stream until the black and white sectors can no longer be seen, and the depth is read from the markings on the line. Readings taken at different sites let students compare water clarity during ecology fieldwork.
Frequently Asked Questions
How long is the line on the Secchi Disk?
The rot-proof polymer line is approximately 72 feet (22 m) long, with a marking at each foot, and is wound on a polymer foam bobbin.
