The distance the human eye can see through a given medium, such as air or water, under certain environmental conditions.
In aquatic sciences, visibility is usually measured in meters with a Secchi disc. Visibility in water can be an indication of water turbulence. As water moves within a given area, it stirs up sediment and nutrients that have settled onto the area’s bottom – an action similar to shaking a snow globe. Visibility can also be an indication of how much productivity is occurring in the aquatic system. For example, all other variables being equal, a pond that is rich in plant and animal life will likely have a lower visibility than a pond that has very little life. This is because there are more plankton and particulate matter in the water column of the pond rich in life – similar to the difference between looking down a crowded street and looking down the same street when it is empty of people.