This is intended to provide a layman’s level of understanding on water quality. The topic at length is not for the faint of heart and becoming a knowledgeable expert will turn you into a hydrologist. If you are interested in that level of detail please see our other education article “Becoming a Hydrologist”.

When we talk of water quality there are a few things we are looking for. Please note that this is not an exhaustive list.

Picture of a creek covered by an algae bloom

An algae bloom


  • The presence and concentration of algae.
    1. While some algae is important for any healthy body of water, too much can cause horrible damage to an eco-system. If too many nutrients that algae feed on are present in water you can have an ‘algae bloom’. These blooms can kill fish and make the water toxic.
    2. Too few nutrients (caused typically by not enough sunlight) can result in not enough algae to convert carbon dioxide into oxygen and provide food for the fish and lead to sterile waters where no fish or animals live.
  • How conductive (or salty) is the water?
    1. Animals have different tolerances for salt in their water. Most have a specific salinity range that they can survive at, and will die if kept outside of that range.
    2. A quick change in conductivity can be the result of the introduction of pollution, like an oil spill, agricultural runoff, or a sewage leak.


  • Dissolved Oxygen levels
    1. Fish breathe dissolved oxygen through their gills. This oxygen is created by plants and bacteria.

      A fish kill – none of the fish are safe to eat.

    2. Saltwater holds less oxygen than freshwater and is one of the reasons why fresh water fish have trouble surviving in salt water.
    3. If oxygen levels rapidly drop, whole lakes can loose their entire fish population.
    4. If oxygen levels rapidly increase fish can get what is called ‘gas bubble disease’. This disease can be fatal in as little as three days. High dissolved oxygen levels occur in highly aerated waters, such as near a hydropower dam or waterfall, or in water with too much algae.
    5. Areas with no dissolved oxygen are known as dead zones.


  • The pH of water
    1. pH is a scale of measurement used to determine if water is Acidic, Basic or Alkaline.
    2. Optimum levels of pH for fish are from 6.5 to 9.0. Outside of these ranges very few fish can survive.
    3. Humans can only safely drink water between 4 and 10. Below 2.5 will cause irreversible damage to skin and organ linings. Levels above 9.5 can dissolve pipes and increase the quantity of metals ingested.



  • What is the temperature? How deep does the sun’s light and warmth penetrate?
    1. The variables determine at what levels plants can use photosynthesis to create oxygen.
    2. Too high of a temperature can cook and kill the plants.
    3. Too low of a temperature will starve plants and cause them to consume oxygen instead of producing it.
    4. Removing trees from the sides of riverbanks increases the temperature of the water, killing some plants and reducing food for fish. Some fish, like trout, require colder temperatures.




Fondriest Environmental, Inc. “Algae, Phytoplankton and Chlorophyll.” Fundamentals of Environmental Measurements. 22 Oct. 2014. Web. <>.

Fondriest Environmental, Inc. “Conductivity, Salinity and Total Dissolved Solids.” Fundamentals of Environmental Measurements. 3 Mar 2014. Web. < >.

Fondriest Environmental, Inc. “Dissolved Oxygen.” Fundamentals of Environmental Measurements. 19 Nov. 2013. Web. < >.

Fondriest Environmental, Inc. “pH of Water.” Fundamentals of Environmental Measurements. 19 Nov. 2013. Web. < >.

Fondriest Environmental, Inc. “Solar Radiation and Photosynethically Active Radiation.” Fundamentals of Environmental Measurements. 21 Mar. 2014. Web. < >.