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Stream Water Quality

Partial Listing of General Surface Water
Physical and Chemical Standards
General Guidance for Educational Purposes

The following is a brief guide related to the interpretation of surface water quality data as it relates to interpreting or evaluating the quality of a Surface Water Source.

Parameter Range
Dissolved Oxygen 4 mg/L or more is desirable
Some Guidelines
• Warm water fish - >5.0 mg/L
• Cold water fish - > 6.0
• Spawning season - > 7.0
• Estuarine biota - > 5.0
• Primary Contact - > 3.0
• Secondary Contact - > 3.0
Temperature 15 to 25 °C
pH 5.0 to 9.0 for most fish
6.5 to 8.2 best fishing waters
Total Hardness
as mg CaCO₃/L
0 - 60 Soft Water
61 -120 Mod. Hard Water
121 - 180 Hard Water
181+ Very hard Water
Nitrate (NO₃)
mg as N/L
< 0.1 mg/L Unpolluted Water
Ammonia (NH₃)
mg as N/L
0.1 mg/L and up - Domestic or Agricultural Waste
0.06 mg/L - Can cause gill damage
0.2 to 0.3 mg/L - Lethal to Trout
Phosphorous mg P/L Recommended Max. is 0.1 mg/L
(not for health reasons)
Chlorides (mg Cl/L) 170 mg/L or less - best for fish
Fecal Coliform
(colonies/100 ml)
less than 20 colonies/100 ml is desirable.
200/100 ml Max for direct contact recreational use.
1000/100 ml Max for indirect recreational use.
(biochemical oxygen demand - 5 day)
1 to 2 mg/L - Very Clean
3 to 5 mg/L - Mod. Clean
over 5 mg/L - Serious Pollution

Note on Dissolved Oxygen

Environmental Effects: The introduction of excess organic matter or soluble organic materials may result in a depletion of oxygen from an aquatic system through chemical or biological oxygen consumption or demand. Exposure to low dissolved-oxygen levels (< 5 - 6 mg/l ) may not directly kill an organism, but will increase its susceptibility to other environmental stresses. Exposure to < 30% saturation (<2 mg/l oxygen) for one to four days may kill most of the biota in a system. If oxygen-requiring organisms perish, the remaining organisms will be air-breathing insects and anaerobic (not requiring oxygen) bacteria. Warmer water (thermal pollution) can also deplete the dissolved oxygen levels as warmer water cannot hold as much dissolved oxygen. 

Recreation: If all oxygen is depleted, aerobic decomposition ceases and organic decomposition or processing is accomplished through anaerobic reactions. Anaerobic microbes obtain energy from oxygen bound to other molecules such as sulfate compounds and can result in the mobilization of many otherwise insoluble compounds, such as the iron in Acid Mine Drainage. The breakdown of sulfate compounds will often impart a "rotten-egg" smell to the water, affecting its aesthetic value and preventing recreational use.

Warm Water Fish: Prefer water temperatures ranging between 18-29 °C (65-85 °F); includes fish such as smallmouth bass, largemouth bass, and bluegill.

Cold Water Fish: Fish such as trout and salmon; preferred water temperature ranges between 7-18 °C (45-65 °F); coolwater fish, such as striped bass, northern pike, and walleye, have a range between that of cold water and warm water fish.

Note on pH

Environmental Effects: A reduction in pH (more acidic) may allow the release of toxic metals that would otherwise be adsorbed to sediment can be released into overlying water. Once mobilized, these metals are available for uptake by organisms which can affect the rate of biological activity and level of the pollutant in the environment. Metal uptake can cause extreme physiological damage to aquatic life. Aluminum concentrations of 0.1 - 0.3 mg/l will increase mortality, retard growth, gonadal development, and egg production of fish. Even if the aluminum availability is low, recent studies have shown that acidity alone may cause mortality in developing brook trout.

Acidification of the aquatic system can shift the biological community to one that is less desirable for recreational and aesthetic uses, it can reduce decomposition rates and nutrient cycling, reduce the variety and distribution of the biological organisms that create a health ecosystem, and make other compounds like ammonia and trace metals more toxic.

More on Turbidity

Environmental Effects: Turbidity is not commonly used to evaluate surface water quality. Turbidity is basically a measure of the amount of light intercepted by a given volume of water due to the presence of suspended and dissolved matter and microscopic biota. Increasing the turbidity of the water decreases the amount of light that penetrates the water column, which can then cause changes in the aquatic ecosystem.

These changes could result in a reduction in photosynthetic activity of phytoplankton, algae, and macrophytes, which would reduce the primary productivity of the system and may result in causing less favorable Cyanobacteria (blue-green algae) to become established. Turbidity can also result in the reduction of dissolved oxygen, destroying the habitat of macroinvertebrates, and causing gill damage/abrasion.

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