Conductivity is a measure of the amount of dissolved solids which are primarily ions. Meter detects the amount of electricity that is conducted by the water sample. The larger the amount of ions the greater the amount of electricity conducted and hence conductivity of the sample. Units are µmhos/cm or µS/cm. Values typically range from 40 to 140 in the river. Sites greatly impacted by stormwater (runoff which contains high levels of dissolved solids) have values as high as 600.