Water Quality Factors

Nitrates
Nitrate is an essential life nutrient for aquatic plants. It's a "limiting nutrient," meaning that when levels of nitrate are low plants use it up and stop producing and when levels are high they overproduce. Overproduction of algae in particular causes problems, as it lowers light levels in water, leading to the decay of plants which can no longer photosynthesize. In these circumstances the decay leads to an overproduction of bacteria which uses the dissolved oxygen in the water and can endanger aquatic animals.

pH
pH refers to the level of acidity in a substance. The scale runs from ) to 14--0 is most acidic, 14 is most basic. Pure water is exactly neutral, a 7, but chemical runoff from human activities as well as naturally occuring minerals can change the level. Fish can only live in a range of pH roughly from 6.5 to 8.5, and therefore shifting pH levels can be very dangerous to aquatic health.

Conductivity
Conductivity in water is determined by the level of dissolved solids in the water, because pure water does not conduct energy well. The level of dissolved solids is, in turn, a concern because of water cleanliness.

Turbidity
Turbidity refers to the degree to which a body of water is transparent, ie how much sediment is suspended in the water. This determines how much sunlight is let into the body of water and therefore how much plants photosynthesize, which in turn affects the water's DOC, or dissolved oxygen content. Sediment can also cause damage to bottom-feeding animals as it settles to the bottom of the stream if levels are too high.

Dissolved Oxygen
This refers to the amount of molecular oxygen which exists in the body of water. This oxygen enters the water through the mixing of water and air, as at rapids or waterfalls in the stream, and through the photosynthesis of underwater plants. It is necessary for fish to survive and most other elements of stream health are measured in terms of their ability to positively or negatively affect DOC levels.

Temperature
Stream temperature, like air temperature, is significant to the creatures who live in it. It influences the amount and diversity of aquatic life--certain animals and plants live only in warm or only in  cool waters, for example. Generally, a rise in water temperature raises nutrient and food levels for aquatic animals and plants, but when waters become too warm they often don't contain enough dissolved oxygen to support life as it evaporates from the body of water.

Alkalinity
Alkalinity refers to the ability of a stream to neutralize acids which enter it. Streams with high alkalinity are "well buffered" so that large amounts of acid can be added without changing the stream's pH, and this is considered to be a positive thing as it improves the water's chemical stability.

E. coli
E. coli is bacteria found in the digestive system of warm-blooded animals. While not itself damaging, it is an indicator of other bacteria which is both harder to measure and far more dangerous, particularly to humans who may use the body as a source of drinking water. E. coli poisoning can cause sever digestive problems, kidney damage, and death.