ABSTRACT
Optical measurements have contributed to defining the trophic status of inland waters, the primary productivity and irradiation characteristics of natural waters, as well as temporal changes in aquatic composition. Unanticipated changes in the clarity of Great Lakes waters have resulted in scientific focus being quickly directed toward aquatic regions at risk. The Great Lake data will be used to illustrate briefly the nature of the optical measurements and the contributions the routine use of submersible optical devices continue to provide to large lake surveillance protocols. As such, the term is highly subjective in nature, and, apart from the eyesight of the submerged viewer, the major factors governing the numerical value of the subsurface sighting range are the optical properties of the water column. Large values of subsurface sighting range are associated with clear waters, while small values are associated with turbid waters.
