Secchi disc readings were used to determine turbidity at the reef site on a regular basis. The rope was marked at five foot intervals to determine at what distance the disc could no longer be seen on a horizontal axis.

Image ID: reef0145, NOAA's Coral Kingdom Collection
Location: Pokai Bay, Oahu
Photo Date: June 1969
Photographer: Dr. James P. McVey, NOAA Sea Grant Program


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