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The black and white colors on the Secchi Disk disappear as it is lowered into the water.

The Secchi disk is widely used as a basic indication of water clarity—it provides a convenient method for measuring light penetration below the surface of a body of water. Water clarity is important to the growth of submerged aquatic vegetation (SAV) and aquatic habitats. If water clarity is measured through the season and from year to year, trends may be observed. Improving water quality trends indicate that restoration efforts are working.

A Secchi disk is an eight-inch (20 cm) disk with alternating black and white quadrants. It works by lowering the disk into a body of water by hand using a graduated line. This enables the observer to determine how deep they can see into the water.

How to Monitor with a Secchi Disk

Download the Field Data Sheet to use while you are making your measurements in the field.

  1. Without wearing sunglasses, take a position in a shaded area alongside the water around mid-day. The depth of the water at the sample location should not exceed six feet.

  2. Lower the Secchi disk into the water on a graduated line.

  3. Record the depth at which the Secchi disk is no longer visible as D1 (to nearest tenth of a meter).

  4. Raise the Secchi disk and record the depth at which the disk reappears as D2. 

  5. The average of the D1 and D2 measurements is the Secchi depth (SD). Record Secchi depth on the field log.

  6. Measure and record the other parameters.

Collect Other Parameters

While at the Secchi disk sampling location, please collect the following:

 

Submit Your Field Data

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Sampling Results
Secchi Depth (m)
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Watershed Management and Monitoring

County Office Building
111 West Chesapeake Avenue
Room 305
Towson, Maryland 21204

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410-887-4804

Director

Horacio Tablada