Secchi Disk Depth One of the most commonly used measurements for
water clarity is the Secchi disk depth (pronounced she SEHK-ki)
. The Secchi disk is a simple and inexpensive device used by
both citizens and scientists for measuring water clarity. The
device generally consists of a 20-centimeter (8-inch) disk made
of wood or plastic. Some are painted with alternating black and
white quadrants, or they can be solid white. A non-stretching
piece of rope or light chain is attached through the center; the
rope is marked in increments of feet or meters. A small weight
is attached beneath the disk so that it will sink quickly and
the line will remain taught while measurements are being made.
The disk is lowered below the surface until it just disappears
from view; that depth is referred to as the Secchi disk depth.