Background
Father Pietro Angelo Secchi, scientific advisor to the Pope, was asked by Commander Cialdi, head of the Papal Navy, to test a new transparency instrument. This instrument, now named the “Secchi (rhymes with ekki, or Becky) disk, was first lowered from the papal steam yacht, l’Immacolata Concezione (The Immaculate Conception) in the Mediterranean Sea on April 20, 1865. One of the best aspects of the Secchi disk is that the information it provides is easily interpreted by volunteers and can be used to detect water quality trends in lakes.
There have been many revisions to the first disks used by Secchi in terms of size and color. The two most common colors variations in use today are the all-white disk and the black and white quadrant version disk. In Montana, we use the black and white quadrant, 8 inch diameter metal disk.
Water transparency is a quick and easy measurement that tells scientists a lot about a lake’s water quality. First, it indicates the amount of light penetration into a lake. Second, Secchi transparency provides an indirect measure of the amount of suspended material in the water, which in many cases is an indication of the amount of algae in the water. Long-term transparency monitoring by NMLN volunteers provides a valuable basis for detecting trends in water quality. Generally, the sooner water quality problems are detected, the easier and less expensive it is to restore the lake to its previous state.