Water pollution and the attendant ecological causes may be assessed based on a
variety of parameters. The most common of concern in highly polluted waters are
measures of oxygen demanding substances, such as BOD5 and COD. Secondly are
suspended solid materials which limit light penetration, cause sedimentation and
smothering of the benthic organisms, and abrade fish gills.
Other groups include nutrients, oils, heavy metals such mercury and persistent
chemicals, such as pesticides