Secchi disk
= Secchi disk
{wiki=Secchi_disk}
A Secchi disk is a simple and effective tool used to measure water transparency in bodies of water. It consists of a circular disk, usually about 20 centimeters (8 inches) in diameter, that is divided into black and white quadrants. The disk is lowered into the water on a rope or cable until it becomes invisible to the observer, who then records the depth at which this occurs.