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August 8, 2016

This EarthWord is clear as mud...

EarthWords is an on-going series in which we shed some light on the complicated, often difficult-to-pronounce language of science. Think of us as your terminology tour-guides, and meet us back here every week for a new word!

Image shows a USGS scientist standing in brown water with red and brown cliffs in the background
Here, U.S. Geological Survey (USGS) hydrographer John Gray is collecting a suspended-sediment water sample from the highly turbid Little Colorado River in the Grand Canyon. Credit: USGS.

The EarthWord: Turbidity


  • It’s not often that we can make a joke about a word being literally as clear as mud, but today we get to. Turbidity, which can make water appear cloudy or muddy, is caused by the presence of suspended and dissolved matter, such as clay, silt, finely divided organic matter, plankton and other microscopic organisms, organic acids, and dyes.


  • Turbidity originates from the Latin turba, meaning “turmoil.” It’s possible that turba itself came from the Ancient Greek tyrbe, which also meant “turmoil.”

Use/Significance in the Earth Science Community:

  • Turbidity is an important measure for surface water, because it shows how many things are in the water, namely, suspended sediment. That, in turn, can affect how much light gets to organisms that need it; the quality of habitat for the organisms that live in the water; and even how fast a lake might fill in with sediment.

  • In addition, suspended sediment can provide food and shelter for pathogens that can affect human health.. Although turbidity itself is not a direct indicator of health risk, numerous studies show a strong relationship between removal of turbidity and removal of protozoa.


  • USGS measures turbidity as part of its Office of Water Quality. During both routine water quality monitoring and flood response, our scientists and technicians measure turbidity using a variety of tools.

  • In addition, some of our streamgages have the ability to measure turbidity.

  • USGS monitored turbidity on the Elwha River in Washington when two dams were removed to restore the ecological health of the river.


Next EarthWord: Feeling salty over our bad jokes? Then this EarthWord’s for you!

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