Make a secchi disk - How to
20 cm diameter circle of acrylic disk 3/8” or 1/2” in thickness
(aluminum or steel may be substituted, but wood is not recommended)
15 cm circle or square of 1/8” galvanized steel (used to weight the disk)
hand drill
eye bolt – 5/16” x 2”
two flat 5/16” washers
one locking 5/16” washer
two 5/16” nuts
flat black rust resistant spray paint
flat white rust resistant spray paint
masking tape
nylon rope (cut long enough to be the depth of your lake deep spot.
Avoid cotton rope because it stretches)
1. Divide the 20 cm acrylic disk into quadrants using masking tape. Spray paint alternating
quadrants black and white, so that you have a disk that is similar to that pictured below.
Let the paint dry. Apply a second coat of paint if necessary.
2. Drill a hole of 3/8’ through the center of the
acrylic disk and the galvanized steel disk.
3. Assemble disks with eyebolt (5/16” in
diameter). Use flat washers between disk and
nut, and between steel plate and locking washer.
Use 5/16” nuts at the top of the eyebolt and to
bolt the steel plate on the underside of the
acrylic disk.
4. Attach a brass chain or rope calibrated by 0.5
meter increments to the secchi-disk to use in the
(Note: If rope is used, avoid using cotton rope or clothesline since it stretches when it is
wet. Use non-stretching white plastic coated wire-core clothesline. Make sure to bend
and straighten the line before you buy it to make sure that it will lie straight. Calibrate
the rope at 0.5 meter increments using permanent pen, or by tying knots at each 0.5
meter interval.)
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