Quote Originally Posted by itsbob View Post
People refer to water clarity by how far through the water you can see an object.Easiest way is to drop a lure into water and let it drop to depth you can't see it anymore.Then pull lure out of water and measure the length of line out.Another common reference to water clarity is being able to see cavitation plate or prop of your outboard.If water clarity less than a foot,it is really difficult to catch fish.More than a foot,you can catch with a crankbait.
That's a good explanation. I would just add that you use a white lure with that method. A Secchi disk is used in the scientific method. It is a 30cm disk divided into 4 quarters alternating black and white that is lowered into the water until the white is no longer visible. A white lure is a decent proxy to estimate visibility.