what is secchi depth
The depth at which the disk is no longer visible is taken as a measure of the transparency of the water. This measure is known as the Secchi depth and is related to water turbidity.Since its invention, the disk has also been used in a modified, smaller 20 cm (8 in) diameter, black and white design to measure freshwater transparency. Secchi disk measurement should always be taken off the shady side of a boat or dock between 9 am and 3 pm The period for best results is between 10 am and 2 pm. The same observer should take Secchi depth measurements in the same manner every time.