Turbidity is a measure of the amount of suspended material in the water and is a direct assessment of the penetration of light through the water. Turbidity is caused by living organisms such as algae (minute plants) and zooplankton (small animals), and by nonliving components such as suspended clay or silt. The lower the turbidity reading the murkier the water and therefore the more shallow the light penetration.

A certain amount of turbidity is required in dams and ponds. In very clear water freshwater, crayfish tend to hide during the daylight hours rather than feed. There is also the risk of increased predation from birds etc. However, too high a turbidity can also cause problems. For example, if a high turbidity is due to clay particles in the water then the light penetration is reduced. As a result of this, photosynthesis by the algae in the water is reduced and limited to the top layer of water. This can result in a reduction of the amount of oxygen in the water and, in particular, deoxygenation of the bottom water layer. The pond may also become thermally stratified.

On the other hand, if the turbidity is caused by algal blooms in the pond, then this also affects the oxygen levels in the water. For example, if the bloom is too large, then large amounts of oxygen are produced during the day by photosynthesis. During the nighttime, the plants respire and consume oxygen which, under certain conditions, also leads to depletion in the oxygen levels and therefore possible loss of stock.