Turbidity is a measure of the cloudiness of water. It is caused by tiny particles, such as silt and clay, organic matter and microscopic plants and animals suspended or floating in the water.

High turbidity reduces the penetration of sunlight into water and can limit photosynthesis and hence the growth of aquatic plants. It therefore affects the animals that rely on these plants for food and shelter.

Turbidity can make it difficult for animals to breathe by clogging or damaging their gills, or making it difficult for animals that filter-feed to collect food. As the suspended particles settle to the bottom they can also smother animal habitats, eggs and larvae.

Turbid water also heats up more than clear water, which can reduce the amount of dissolved oxygen available for animals to breathe. Over time, unatural levels of turbidity can reduce the biodiversity in a waterway.

Causes of turbidity:

  • soil erosion due to heavy rainfall or floods
  • erosion of the banks of a waterway
  • sediments from building sites
  • stormwater
  • loss of vegetation cover especially within the riparian zone