Developed in 1865 by Angelo Secchi, the first Secchi disk was used to measure transparency in the Mediterranean Sea. Today’s Secchi disk is a simple and effective tool that allows you to determine the productivity of freshwater lakes.
Constructed of sturdy white plastic, the disk alternates between white and black printed quadrants. Fused to the bottom of the disk is a weight to help it sink. Attached at the center of the top side is the 72-foot cord which includes a polymer foam bobbin for visibility. Excess cord can easily be contained using the spool.
Measurements are taken by lowering the Secchi disk until it can no longer be seen. This point is known as the Secchi depth. Because light can penetrate deeper in clear water, the further the disk sinks, the higher the Secchi depth, which indicates clearer waters. The presence of high concentrations of algae and particulate in the water decrease visibility, in turn, decreasing the Secchi depth measurement, indicating turbid water.
The Secchi disk is designed for use in shallow water and works best in shaded areas to eliminate glare from the sun. The optimal time to take a reading is between 10 am and 2 pm. A best practice is to use the average of two depth measurements.
Lake transparency can change with the seasons due to temperature and the amount of exposure to sunlight. It is important to take numerous Secchi disk readings throughout the year. During cooler months, a reading once a month is sufficient, but this should be increased to a minimum of every two weeks during summer months. Over time the data will reveal water quality trends. An increase in Secchi depth shows improvement in water quality, while a decrease shows that water quality is declining.
Our Secchi Disk With Lanyard Kit includes everything you need to begin monitoring water productivity:
- Weighted, black and white solid plastic Secchi disc
- 72’ rot-proof polymer cord
- Spool to wind excess cord
- Detailed instruction manual
Our Secchi discs come with a 100% satisfaction guarantee.