Conductivity is a measure of the ability of water to pass an electric current. Salt causes conductivity to go up. Oil causes it to go down.

High salt concentrations can kill fish and other aquatic plants and animals. Oils can also harm these species.

pH determines if the water is basic, acidic, or neutral. Changes in the pH are very important because if the water is too acidic or too basic some species of fish can't live in it.

In the spring, there are a lot of problems in lakes and streams because of melting acid snow. Very acidic lakes and streams cause leaching of heavy metals into water. Some of the metals include copper and aluminum. These metals accumulate on gills of fish making it hard for them to breathe.

Phosphate comes from some household detergents, human wastes, animal wastes, industrial wastes, and human disturbance of the land and its vegetation.

It stimulates the growth of rooted aquatic vegetation and it causes extensive growth of algae.

It affects the fish because too much phosphate causes algae growth and low levels of dissolved oxygen for fish to breathe. It also makes the water unclear and less attractive for humans to use.

Turbidity is the measure of the relative clarity of water. Sources of turbidity include solids such as clay, silt, plankton, industrial waste, sewage, and microorganisms. These solids come from soil erosion, waste discharge, urban runoff, algae growth, and abundant bottom feeders that stir up sediment from the bottom.

As a result of turbidity the river loses its ability to support aquatic life. Sediments can clog fish gills, reduce growth rate, decrease resistance to disease, and prevent egg and larvae development.

Velocity is important because increased velocity means increased turbidity. Heavy rain in industrialized areas, where the water is not absorbed but is simply washed over hard surfaces (pavement, gravel, etc.) and sent directly into a river, cause increases in velocity.

The water temperature of a river influences:

• the amount of oxygen that can be dissolved in water;
• the rate of photosynthesis by algae and larger aquatic plants;
• the metabolic rates of aquatic organisms; and,
• the sensitivity of organisms to toxic wastes, parasites, and diseases.

As water temperature rises, the rate of photosynthesis and plant growth also increases. More plants grow and die. As plants die, bacteria that consume oxygen decompose them. Fish die because of the decrease the oxygen level.