A secchi disk is used to determine:

A secchi disk is a simple and effective tool used to measure the transparency or clarity of water, particularly in recreational and natural bodies of water. When the disk is lowered into the water, the depth at which it can no longer be seen indicates the water's clarity. This measurement is essential for understanding the health of aquatic ecosystems, as clarity often correlates with levels of suspended solids, phytoplankton, and other factors affecting water quality.

Monitoring water clarity is vital for recreational water use, as clearer water generally indicates better aesthetic quality and safety for swimming and other activities. It also plays a role in aquatic life health, as light penetration is crucial for photosynthesis in underwater plants. The use of a secchi disk is therefore directly connected to assessing and managing the recreational and ecological quality of water bodies.