Turbidity is the cloudiness or haziness of a fluid caused by large numbers of individual particles that are generally invisible to the naked eye. It is a measure of water clarity and an important factor in water quality. Turbidity can be caused by suspended solids, sediment, plankton, organic by-products, and other materials. High turbidity levels can reduce the amount of light reaching lower depths in bodies of water, which can inhibit the growth of some forms of aquatic plants and negatively affect species that are dependent on them, like fish and shellfish.

Turbidity can be measured in Nephelometric Turbidity Units (NTU) or Formazin Nephelometric Units (FNU) . There are a number of materials that can cause turbidity, including silt, inorganic and organic matter, clay, algae, and some microscopic organisms. Turbidity can be measured using a turbidity tube, a turbidimeter, or other methods.

Turbidity currents are rapid, downhill flows of water caused by increased density due to high amounts of sediment. These currents can change the physical shape of the seafloor by eroding large areas and creating underwater canyons. NOAA scientists use current meters attached with turbidity sensors to gather data near underwater volcanoes and other highly active geological sites.

In summary, turbidity is a measure of the level of particles in a body of water that can affect water clarity and quality. It can be caused by various materials and measured using different methods. High turbidity levels can negatively affect aquatic life and make water treatment more expensive.