A relatively crude measurement of the turbidity (cloudiness) of surface water. The depth at which a Secchi Disc (Disk), which is about 10-12 inches in diameter and on which is a black and white pattern, can no longer be seen.
SECCHI DEPTH
Meaning of SECCHI DEPTH in English
Environmental engineering English vocabulary. Английский словарь экологического инжиниринга. 2012