The Environmental Importance of the Different Impairments

Fecal Coliform Bacteria | pH | Dissolved Oxygen | Nutrients | Turbidity


Elevated water temperature is a common problem in many streams in Washington. When temperatures are too high it can make the streams uninhabitable for fish and other aquatic animals. Many salmon and trout species will suffer a variety of ill effects, ranging from decreased spawning success to death, when waters are too warm. The optimal temperature for most salmon and trout species is between 12-14˚C (54-57˚F). Temperatures in the range of 23-25˚C (73-77˚ F) can be lethal, depending on the species. The temperature of the water can also affect how much oxygen is dissolved in the water. It is this dissolved oxygen (DO) that the fish need to breathe. The warmer the water, the less DO it can hold. The warmer temperatures also tend to speed up the metabolism of the fish so they require more oxygen for biological functions.

To learn more about temperature and DO check out our focus sheets (Ecology publications):

Fecal Coliform Bacteria

Fecal coliform is a type of bacteria found in the feces of warm-blooded animals. When found in bodies of water it can be an indicator of the presence of other disease-carrying organisms. Fecal coliform bacteria can get into water bodies from failing septic systems and animal waste. High levels of fecal coliform in the water can affect the public health, economy, and environmental quality of a community.

A long history of illness outbreaks and epidemics have demonstrated a relationship between the presence of fecal coliform bacteria and the presence of illness-causing viruses and bacteria, called pathogens. These pathogens can be accidentally swallowed with water. People swimming or playing in water can be exposed to pathogens when they enter the body through small cuts, abrasions or mucus membranes.

Some of the symptoms of illness associated with fecal coliform pathogens are minor, such as upset stomach, diarrhea, ear infections, and rashes. However, some pathogens, such as E coli, hepatitis, and Salmonella, can have very severe health effects. Washington’s water quality standard for fecal coliform bacteria is set to protect public health.

For more on fecal coliform check out our focus sheet:

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The pH is a measure of how acidic or basic the water is (in other words, a measure of the concentration of hydrogen ions). At a higher pH there are fewer free hydrogen ions available than at a lower pH. The pH scale (0-14) is logarithmic; in other words one unit of change in pH represents a tenfold change in the concentration of hydrogen ions. For example, there are 10 times as many hydrogen ions available at a pH of 7 (pH neutral) than at a pH of 8. This affects the chemistry and chemical reactions that take place in the water. The pH of the water also is important to the fish and animals that live in it. The pH of streams should be between 6.5 and 9.0 to protect freshwater aquatic life.

The pH can affect the solubility of nutrients and metal compounds. By affecting the solubility of nutrients, it can change the amount of nutrients available for plant growth. If too many nutrients are available, aquatic plants can grow out of control. When these plants decompose, they can deplete the water of oxygen. The solubility of many metal compounds also changes greatly with pH. Generally, a reduction in pH (more acidic) increases the solubility of heavy metals. When more metals are dissolved in the water, aquatic animals may absorb them faster. Therefore, a lower pH (more acidic) may make these metals more toxic to aquatic life.


Chart showing various pH levels and effects (click on chart to see full view)

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Dissolved Oxygen

Like people, fish and other aquatic organisms need oxygen to live. As air or water moves past an animal’s breathing apparatus (gills or lungs), oxygen is transferred to its blood. It is more difficult to transfer oxygen from water to blood than it is to transfer oxygen from air to blood. Therefore, it is critical that an adequate amount of oxygen is maintained in the water for this transfer to take place efficiently. In addition to being required by aquatic organisms for respiration, oxygen is necessary to help decompose organic matter in the water and bottom sediments. It also is necessary for other biological and chemical processes.

To learn more about DO check out our focus sheet:

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Nutrients, like phosphorus and nitrogen, can increase the growth of plants and algae in water. When higher-than-normal levels of nutrients are present, plants and algae can get out of control and lead to changes in the water’s pH, dissolved oxygen and clarity. In addition, increased algae and plants can be ugly, create odor problems when they die and decompose, and interfere with recreational activities like boating and swimming.

To learn more about nutrients please see our focus sheet:

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Turbidity is the measurement of the light-scattering properties of water. The more suspended solids including algae, soil particles, dissolved solids and other materials in the water, the less clear the water is. When light cannot penetrate into the water, the amount of photosynthesis occurring decreases and therefore the amount of oxygen being produced is reduced. High turbidity can have a negative effect on submerged aquatic vegetation, decrease habitat for fish eggs, and slow or stop egg development (because of silt accumulation in the gravel stream bed). It also makes it harder for fish to catch food.

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Last updated September 2010