Unfortunately, secchi disk data is not always the most reliable. This method can be misinterpreted in monitoring programs because of the number of variables.
For instance: the person taking the measurement; is it always the same person taking the reading, at the same site, the same time of day and same conditions?
Everyone has different eyesight that does change over time. This testing is the predominant method for measuring clarity, but we must be careful and look at these variables before making extremely important determinations.
These are the links to the organizations who presently measure this in Grand Lake.
As always you questions or comments are welcome!