Turbidity is a measure of how clear the water is. Suspended materials include soil particles (clay, silt, and sand), algae, plankton, microbes, and other substances. Turbidity can affect the color of the water. Normally the more turbid a water, the more solids it contains.

Higher turbidity increases water temperatures because suspended particles absorb more heat. This, in turn, reduces the amount of dissolved oxygen (DO) because warm water holds less DO than cold. Higher turbidity also reduces the amount of light penetrating the water, which reduces photosynthesis and the production of DO. As the particles settle, they can blanket the stream bottom, especially in slower waters, and smother fish eggs and other small organisms.

Sources of turbidity include:

• Soil erosion
• Waste discharge
• Urban runoff
• Eroding stream banks
• Excessive algal growth

Optimal temperatures for fish and other aquatic organisms depend on the species: some survive best in colder water, others prefer warmer water. Some aquatic animals are sensitive to changes in water temperature and require a certain temperature range to survive and reproduce. Benthic macroinvertebrates are sensitive to temperature and will move around in the stream to find their optimal temperature.

Temperature affects the amount of oxygen the water can hold (cold water can hold more oxygen than warm). Warm water discharged from factories, sewage plants, or hot city roads can be considered a form of pollution to those creatures that are sensitive to temperature. Temperature also affects the rate of photosynthesis by aquatic plants; the metabolic rates of aquatic organisms; and the sensitivity of organisms to toxic wastes, parasites, and diseases.

Causes of temperature change include:

• Natural weather patterns
• Removal of shading bayou-side vegetation
• Discharge of water used to cool machinery

Urban storm water (it is often warm when it rolls off of the hot streets)

Both phosphorus and nitrogen are essential nutrients for all plants and animals, but even a modest increase in phosphorus can, under the right conditions, set off a whole chain of undesirable events. These include accelerated plant growth, algae blooms leading to low dissolved oxygen, and the death of certain fish, invertebrates, and other aquatic animals.

There are many sources of phosphorus, both natural and human. These include:

• Soil and rocks
• Wastewater treatment plants and runoff from animal manure storage area
• Runoff from fertilized lawns and cropland
• Failing septic systems
• Disturbed land areas and drained wetlands
• Commercial cleaning products

Nitrates are a form of nitrogen, and include ammonia, nitrates, and nitrites. These are essential plant nutrients, but too much can cause problems. Together with phosphorus, nitrates in excess amounts can accelerate eutrophication, causing dramatic increases in aquatic plant growth and changes in the types of plants and animals that live in the stream. This, in turn, affects other things, like dissolved oxygen and temperature. Since the natural nitrate level of water is low, too many can reduce dissolved oxygen levels and can become toxic to warm-blooded animals. Wastewater treatment plants normally have a much higher average level of nitrates.

Sources of nitrates include:

• Runoff from fertilized lawns and cropland
• Failing onsite septic systems, wastewater treatment plants, and runoff from feedlots or animal manure storage areas
• Industrial discharges

All animals breathe oxygen, whether it is oxygen from the air or dissolved oxygen (“DO”) in the water. DO fluctuates naturally, depending on the time of day and the temperature. Cold water can hold more oxygen than warm water. Many aquatic animals are sensitive to the fluctuations of DO or low levels of DO.

Water gains oxygen from the atmosphere and from photosynthesizing plants. Running water, because of its churning, dissolves more oxygen than still water. Wastewater from sewage treatment plants often contains organic materials that are decomposed by microorganisms. These microorganisms use oxygen to breath while they break down organic matter. Respiration by aquatic animals and decomposition of dead plants and animals consume oxygen. If dissolved oxygen levels decline, some sensitive animals may weaken, or die.

Dissolved Oxygen levels fluctuate for different reasons:

• Temperature (cold water holds more oxygen than warm water)
• Thermal discharges (water used to cool machinery will raise the temperature of water)
• Stormwater runoff from farmland or urban streets
• Sewage treatment plant wastewater, feedlots and failing septic systems (because of the bacteria associated with manure)
• Presence of photosynthesizing aquatic plants (Aquatic animals are most vulnerable to reduced oxygen levels in the early morning on hot summer days when the water is hot and aquatic plants have not been producing oxygen since sunset.)

Measuring alkalinity is important in determining a stream’s ability to neutralize acidic pollution from rainfall or wastewater. Total Alkalinity is a measure of the capacity of water to neutralize acids. Alkalinity in streams is influenced by rocks and soils, salts, certain plant activities, and certain industrial wastewater discharges.

pH is a term used to indicate the alkalinity or acidity of a substance. Low pH indicates high acidity while high pH indicates high alkalinity. Many aquatic organisms are adapted to a specific pH range and can die if it varies.

pH affects many chemical and biological processes in the water; different organisms thrive in different pH ranges. Most aquatic animals prefer a somewhat neutral range. A pH value that is too high or too low stresses the bodies of most organisms and can decrease reproduction rates. Low pH can also allow toxic elements and compounds to become mobile and “available” for uptake by aquatic plants and animals. This can produce conditions that are toxic to aquatic life, particularly to sensitive species.

Changes in acidity can be caused by:

• Atmospheric deposition (acid rain)
• Certain wastewater discharge

Fecal coliform: Fecal coliform bacteria are microscopic organisms that live in the intestines of warm-blooded animals. They also live in the waste material, or feces, excreted from the intestinal tract. When fecal coliform bacteria are present in high numbers in a water sample, it means that the water has received fecal matter from one source or another. Although not necessarily agents of disease, fecal coliform bacteria may indicate the presence of disease-carrying organisms, which live in the same environment as the fecal coliform bacteria. Definition from Washington State Department of Ecology

Possible sewage contamination is indicated by the presence of members of two bacteria groups, coliforms and fecal streptococci. These are commonly found in human and animal feces and though they are generally not harmful themselves, they indicate the possible presence of pathogenic (disease-causing) bacteria, viruses, and protozoa that also live in human and animal digestive systems.

Therefore, their presence in water suggests that pathogenic microorganisms might also be present and that swimming and eating shellfish might be a health risk. Since it is difficult, time-consuming, and expensive to test directly for the presence of a large variety of pathogens, water is usually tested for coliforms and fecal streptococci instead.

Sources of fecal contamination to surface waters include:

• Wastewater treatment plants
• On-site septic systems
• Domestic and wild animal manure
• Storm runoff
• In addition to the possible health risk associated with the presence of elevated levels of fecal bacteria, they can also cause cloudy water, unpleasant odors, and an increased oxygen demand.
• http://www.epa.gov/volunteer/stream/