What water clarity tells us

Tracking water clarity is like monitoring your blood pressure - it tells us about the health of a lake or stream. It indicates the amount of light penetration into the water. For streams, a low clarity reading reflects excess sediment. For lakes, a low clarity reading reflect excess algae. Consistently low clarity readings indicate poor water quality and can affect plant, insect, and fish communities and reduce recreational opportunities. Long-term water clarity data collected by citizen water monitors help detect signs of degradation to a lake or stream. It is generally easier and less expensive to restore a lake or stream if problems are detected early.

Tools we use to measure water clarity

Measuring water clarity is quick and easy. Secchi tubes are used to monitor stream water clarity and Secchi disks are used to monitor lake water clarity.

What is a Secchi tube?

To measure water clarity, a Secchi tube is filled with water collected from a stream or river. Looking down into the tube, volunteers lower a weighted disk attached to a string until the disk disappears. The distance at which the disk disappears is the water clarity reading, which is recorded in centimeters. A high Secchi tube reading reflects better water clarity.

Child looks down into top of clear plastic Secchi tube

What is a Secchi disk?

A Secchi disk is an 8-inch, circular, all-white metal plate attached to a calibrated rope. Volunteers take readings by lowering the disk into the lake. Volunteers find the disappearance/reappearance point of the disk as it descends into the water and record the reading in feet. A high Secchi disk reading reflects better water clarity.

Man in boat lowers black and white Secchi disk into lake