Color (as related to water quality)

Measured against a platinum-cobalt standard (PCU or Pt-Co units),
can give an indication of the relative amount of dissolved
organic matter in the water. High coloration, or "bog stain" as
it is referred to, is usually caused by runoff from wetlands or
forested lands. At high values, color may interfere with the
expected phosphorus - chlorophyll - Secchi relationship of a
lake. In general, values between 0-20 are considered clear, 21-50
are considered moderately colored, 51-100 are considered
highly colored, and values greater than 100 can be considered
very highly colored. Based on data from
the ecoregion reference lakes color begins to influence the
phosphorus - chlorophyll - Secchi
relationships above about 50 Pt-Co units, and may strongly
influence the relationship above 100 Pt-Co
units. In highly colored lakes, transparency and chlorophyll
values are often lower than expected based
on the phosphorus values.