Commonly measured water quality parameters are:
Dissolved oxygen (DO)
Dissolved oxygen is required for aquatic life and the water should generally be greater than 80% saturated with dissolved oxygen. Changes in DO indicate organic pollution or photosynthetic activity.
Biological oxygen demand (BOD)
Biological Oxygen Demand is an indicator of organic pollution.
Temperature
The right water temperature is important for aquatic life. Temperature is also an indicator of mixing rates for some discharges.
Conductivity
Conductivity is an indicator of the total dissolved mineral content of water.
pH
Water with a very high or very low pH can be toxic to aquatic life. A pH range of 6.0 to 9.0 is suitable for aquatic plants and animals. pH is an indicator of industrial discharges or photosynthetic activity.
Clarity
Water clarity may affect the amount of light available to aquatic life. Poor water clarity may reduce the ability of plants to photosynthesise, make it difficult for fish or other animals to see their prey and reduce the aesthetic appearance. Measures of clarity are turbidity, black disc and secchi disc.
Suspended solids
The level of suspended solids will affect aesthetic appearance, and is also an indicator of catchment condition and land management practices.
Colour
Colour will affect aesthetic appearance and light availability for plant growth. It is an indicator of the presence of organic matter.
Nutrients
Enrichment of fresh water from nutrients, such as nitrogen, phosphorus or ammonia, can cause excessive plant growth. High levels of ammonia are toxic to aquatic life, especially fish. High nutrient levels may result from either waste discharges or run-off from agricultural land.
Faecal bacteria
Faecal bacteria, such as faecal coliforms, E.coli, and Enterococci, are indicators of pollution by faecal matter. They can provide a measure of the health risk for swimming or other recreational use of water.