Lake Depth Determination

**For the Mass. Department of Environmental Protection-approved SOP, get the pdf file here**

Equipment List

• Secchi Disk (see our water transparency page for description)
• Calibrated line (either surveyor tape or cotton line)
• Lake base map
• Field data sheet and pencils

Measurement Protocol

Lower your Secchi Disk until the line goes slack (disk hits bottom).
Retrieve the line until all slack is removed.
Read depth on line at lake surface.
Record this bottom depth on your lake field sheet .

Maintenance

At the beginning of each sampling season, the calibrated line should be checked for shrinkage/stretching.
Attach a cloth tape measure to the bottom of the calibrated line. Lower the Secchi Disk as deep as you can without hitting lake bottom, feeding the tape measure so it is taut.
Compare the reading on the tape measure with the calibrated line reading. If they don't agree within 10%, you should adjust your Secchi Disk readings accordingly or switch to a fiberglass tape.