Cyanobacteria Causes


What causes cyanobacteria bloom

A bloom does not occur due to only one condition but when several conditions occur at the right time. Although, there are several conditions that can cause a bloom, the tricky thing about cyanobateria is not every condition needs to occur; just a few at the same time.

  • Sunlight
  • Hot Temperatures
  • Low Wave Activity/Stagnant Water
  • Runoff
  • Eutophication



Cyanobacteria is the only prokaryote (a single cell organism that lacks membrane-bound organelles) that is capable of harvesting the sunlight through photosynthesis as energy.


Hot Temperatures

Hotter temperatures warms the water to optimum conditions for cyanobacteria to photosynthesize.


Low Wave Activity/Stagnant Water

Without water moving, nutrient levels can become too high (see Eutrophication below) and it’s easier for cyanobacteria to utilize their aerotope adaptations (visit page What is Cyanobacteria) to find the optimum depth for nutrients and sunlight. This can become a big issue in areas of ponds or lakes that are very shallow.


Excessive Nutrients

Excessive nutrients, in the form of nitrogen and phosphorus, creates an abundant food source cyanobacteria growth. There are many sources that can contribute to excessive nutrients including:

  • Over application of fertilizers
  • Animal/human waste
  • Waste water
  • Improperly functioning septic systems



Runoff due to high rainfall events or irrigation, can wash excessive amounts of nutrients in a water body.



Eutrohphication is when a body of water has accumulated excessive amounts of nutrients (nitrogen and phosphorus). This causes an increase food source for cyanobacteria which leads to it’s abundant growth. With abundant growth, a bloom occurs. The bloom forms on the surface of water bodies where it absorbs sunlight and doesn’t allow sunlight to reach further into the water column. Without sunlight, subsurface algae and plants cannot photosynthesize and begin to decay. Next, bacteria in the water begin to break down the decayed plants which releases more nutrients back onto the water for cyanobacteria to consume. With a larger food source, the bloom can continue to grow, producing an overabundance of oxygen as it does. At night, without sunlight, photosynthesis stops and oxygen levels can drop below what is needed to sustain aquatic life. The decay of these organisms continue the cycle of adding nutrients back into the system.