1. WATER QUALITY Vol 3: Biological Characteristics

2. I. Biological Characteristics
The composition of the community of organisms living in and around a body of fresh water

3. II. EPT Index
While we look at the aquatic community as a whole (the variety of plants, animals, microbes, etc.) that live in a freshwater ecosystem
Macroinvertebrates- large insects, snails, crustaceans and worms can tell us the most about water quality.
EPT INDEX- is a measure of water quality as indicated by three types of insect larva that are especially sensitive to pollution

4. III. Indicator Species
Tolerant- these animals can handle poor water quality, such as low oxygen levels and chemical pollution
Slightly Tolerant-these animals can handle moderate levels of pollution and oxygen, so they indicate fair water quality.
Intolerant-these organisms require perfectly clean water with high oxygen levels. They indicate good water quality.

5. IV. What Affects the Quality of Surface Water?
The overall quality in a given water body is determined by a combination of four categories:
Water chemistry
Sediment chemistry
Physical habitat
Biological community