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Found a graph of this on a USGS river site.

Specific conductance, water, unfiltered, microsiemens per centimeter at 25 degrees Celsius

Most recent instantaneous value: 580 04-25-2016 19:30 MDT

Is this indicating the visibility?
 

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Found a graph of this on a USGS river site.

Specific conductance, water, unfiltered, microsiemens per centimeter at 25 degrees Celsius

Most recent instantaneous value: 580 04-25-2016 19:30 MDT

Is this indicating the visibility?
No, this does not report visibility, i.e. suspended sediment and particles in the water.

Instead, it reports the amount of dissolved salts.

ions from dissolved salts will help the water conduct electricity, which is what the conductance reported in units of microsiemens per cam is measuring.

j
 

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No, this does not report visibility, i.e. suspended sediment and particles in the water.

Instead, it reports the amount of dissolved salts.

ions from dissolved salts will help the water conduct electricity, which is what the conductance reported in units of microsiemens per cam is measuring.

j
Yep salts and other inorganic materials with charges like sulfides and carbonate compounds and other dissolved solids will also affect specific conductance (often mistakenly called conductivity which is a slightly different measurement).
 

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Pretty much what the others have said. To add to it, it's generally the preferred measurement to check on possible pollution where the pollution wouldn't necessarily cause visible symptoms or pH fluctuations.

While streams may have higher or lower readings based on general water quality, a sudden spike usually indicates some sort of pollution. I have a device that tests various aspects of water (including temperature, pH, and conductivity) that I originally obtained with the goal of monitoring a few local streams most at-risk for degradation due to fracking, but I have also used it at other times to test out everything from suspicious tap water to trout streams.

specific conductance (often mistakenly called conductivity which is a slightly different measurement).
The difference, for those interested, is that conductivity is a measure of how readily a given sample will conduct electricity while specific conductance is a measure of the same attribute at a fixed temperature of 25C. This aids in apples-to-apples comparisons, and can be obtained from a conductivity reading by using a chart. For practical purposes, stream readings are a measure of conductivity, as their temperature is not regulated to a set 25C. (Then again, I suppose if a stream was flowing at exactly 25C, the conductivity reading on that stream would indeed be that water's specific conductance.)
 
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