1. a) Balanced environment: Intolerant organisms are many in number and species, or more in numbers than other forms present.

   Intolerant present >50%

   Moderate, facultative and tolerant usually present < 50%

2. b) Unbalanced environment: Intolerant organisms are less in number than other forms combined, but combined with moderate forms, they usually outnumber tolerant forms.

   Intolerant present < 50% but >10%

   Moderate, facultative and tolerant usually present > 50%

3. c) Semi-polluted environment: Intolerant organisms are few or may not be present. Moderate and/or facultative organisms present.

   Intolerant present >10%

   Moderate, facultative and tolerant usually present > 90%

4. d) Polluted environment:

   1. 1) Intolerant organisms absent, only tolerant organisms present or no organisms present.

      Tolerant present = 100%

   2. 2) Organisms which are not adapted to inhabit a polluted environment are occasionally collected as a result of factors produced by the drift and are not representative.

Aquatic environments are classified according to the following: