The Secchi Disk
• A useful device for evaluating water transparency is the Secchi disk.
• Using this disk has the advantages of simplicity and immediate results.
• The Secchi disk itself provides no information about the reason for variation in water clarity.
• Water color is also a factor determining the depth of visibility of the Secchi disk, and recorded observations should include notes on water color that may relate to types of algae present.
• Also, readings should only be taken during the high sun period when light penetration is greatest.
• Between 10 A.M. and 2 P.M. is the optimal period.
• For best accuracy and precision 6–10 Secchi measurements should be averaged and corrected for solar altitude before attempting to compare data from different lakes.