Water Quality Monitoring: Algae


  • Algae, also known as phytoplankton, are tiny, single-celled plants.
  • The abundance of algae is controlled by factors such as light, salinity, water temperature, and nutrient levels. An algal population explosion is known as a "bloom."
  • High concentrations of algae will raise the dissolved oxygen concentration during the day while algae photosynthesize, but oxygen concentrations may drop off steeply overnight as algae consume oxygen or decompose. Aquatic animals may suffocate as a result.
  • The photosynthetic process may also raise the pH to uncomfortable levels. Decaying algae can also cause odor problems and attract flies.
  • Urban creeks, which are often poorly shaded and well feed with runoff from fertilized yards and home car washes, are especially susceptible to algal blooms.


Observe the creek at the sampling site and classify the algae into one of the five categories below:
    Conditions vary from no nuisance bloom algae to small populations present.
    Some nuisance bloom algae visible to the naked eye but present at low to medium levels.
    Nuisance algae sufficiently concentrated that filaments and/or balls of algae are visible to the naked eye. May be widely scattered streaks of algae on the water surface.
    Scattered surface blooms
    Surface mats of nuisance algae scattered; may be more abundant in localized areas if winds are calm. Some odor problems.
    Extensive surface blooms
    Large portions of the water covered by surface mats of nuisance algae. Windy conditions may temporarily eliminate mats but they will quickly redevelop as winds become calm. Odor problems in localized areas.

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