Water depth

WATER DEPTH is the measurement of the depth of a waterbody from the surface to the top of the bottom sediments. Water depth can vary substantially within a waterbody according to its morphology (shape).

One way to measure water depth is to use a weighted Secchi disc. The Secchi disc is attached to a string or cord that is marked in one-foot increments. The weighted disc is dropped down until it hits bottom and then the distance is determined by measuring the length of the rope between the bottom and the surface of the water. These measuremetns are then recorded for future reference.
Water depth can also be measured using a device called a fathometer which bounces (sonar?) pulses off the bottom and electronically calculates the depth.

Water depth readings taken continuously along a number of transects (shore-to-shore trips across the waterbody) may be used to calculate an average lake depth. The calculated average lake depth is approximately the same as the lake's average depth, and is referred to as the lake's mean depth.

See also:
Mean depth;
PVI (Percent Volume Infested or Inhabited);
PAC (Percent Area Covered);
and Submersed aquatic plants

The information on this page was derived in part from the following publication of
Florida Lakewatch of the University of Florida Department of Fisheries and Aquatic Sciences.
This booklet may be downloaded in its entirety as a PDF file by clicking here:

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This project is a collaboration of
the Center for Aquatic and Invasive Plants, University of Florida,
and the Bureau of Invasive Plant Management, Florida Department of Environmental Protection