Water clarity is an important indicator of a waterbody's overall health.  There are two main components that make up clarity, true color (what is dissolved in the water) and turbidity (what is suspended in the water).  In early spring and summer, the primary component found within the water column is suspended solids.  As spring moves into summer and the water column warms, algae becomes the primary component.

Water clarity is typically measured using a Secchi disk.  The disk is lowered into the water column until it is no longer visible and then raised until it becomes visible.  A reading known as the Secchi depth is taken (in meters) at the point where the disk disappears from sight.

In order to achieve certain water quality standards, the RAP set a target range for average summer Secchi depths in both the Fox River and Green Bay.  A Secchi depth of 0.7 meters or 1.3 feet must be achieved if the Fox River and Green Bay are to support healthy populations of submerged aquatic vegetation.  For waters to meet the state swimming standard, an average Secchi depth of 1.3 meters or 4 feet must be achieved.  From the graph below it is clear that the Fox River and Green Bay are not meeting these standards.