What causes an algae bloom?

Last updated on June 13, 2022

Algae are a natural part of all aquatic ecosystems, but prolific growth can cause a dense mass of algae (called a bloom) to form.

Algae blooms can occur when a combination of suitable environmental conditions exist for abundant algal growth (e.g., increased nutrients, warmer temperature, abundant light, and stable wind conditions). When these conditions are favorable for one species over another, it allows for one organism to become dominant and form a bloom.

Some human activities (such as agricultural run-off or poorly functioning septic systems) can make blooms more likely, and excessive amounts of nutrients within a lake can markedly increase the risk and severity of algal blooms. However, excessive nutrients may not lead to a bloom if other factors are unfavourable. For example, in a turbid shallow lake there may be insufficient light to support a bloom despite having high nutrient concentrations and warm water. 

Table: Algae bloom examples
Cyanobloom on Chimney Lake, 2020

Cyanobloom on Chimney Lake, 2020

Cyanobloom bloom on Ellison Lake, 2015

Cyanobloom on Ellison Lake, 2015

Environmental conditions contributing to algal blooms

There are many causes for algal blooms in freshwaters and it is often difficult to pinpoint specific reasons why a bloom forms. In many cases, a set of unique environmental conditions occur in a waterbody, which can lead to a particular species dominating and triggering a bloom.

While bloom formation is waterbody specific, the most common factors for bloom formation are timing, nutrients, temperature, light, and stable conditions.

Icons showing timing, nutrients, temperature, light, and stable conditions

 


 

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