By Pam Saunders

Lake Windermere Ambassadors

Often called blue green algae, naturally occurring cyanobacteria play a crucial role in photosynthesis and nutrient recycling. However, their overgrowth in freshwater bodies can have detrimental consequences on the environment and public health. Let’s look closer at their ecological significance and the causes and consequences of rapid growth.

Cyanobacteria are among the oldest life forms on Earth (over 3 billion years). They are microscopic bacteria that perform photosynthesis – using energy from sunlight to convert water and carbon dioxide into organic compounds, releasing oxygen in the process. This oxygen is vital to aquatic ecosystems where it will be consumed by organisms, fish, and aquatic plants. 

In addition to producing oxygen, cyanobacteria can take nitrogen from the air and convert it to forms that can then be used by other organisms. This nutrient cycling is an important role for cyanobacteria because it maintains the nutrient balance required in aquatic ecosystems.

Clearly cyanobacteria are a part of a healthy aquatic ecosystems, but their rapid and excess growth (sometimes called a bloom) can lead to many negative consequences for the environment and public health.


• Excessive nutrient inputs, such as phosphorus and nitrogen, from sources like agricultural and golf course runoff, sewage, and industrial discharge. These supply the fuel needed for blooms to rapidly grow. 

• Warm water temperatures create hospitable conditions for cyanobacteria causing blooms to thrive. This is more of a concern during warmer summer months, fall and with global warming. 

• Still or slow-moving water bodies are more susceptible to cyanobacteria booms because they lack circulation which allows the organisms to form on the surface in a dense layer (called algae mats).

• A disturbance to the lake’s natural hydrology, such as the construction of a dam or a diversion of the water, can disrupt the natural balance and create the conditions needed for a harmful algae bloom.


• A decline in water quality. As cyanobacteria blooms take off, they may turn the water a blue-green colour leading to a decrease in water clarity. This can block sunlight from submerged plants and hinder aquatic life. Other varieties may produce different bloom colours such as brown, blue, white, and red or may resemble “pea soup”.

• Production of toxins. Some species of cyanobacteria can produce toxins harmful to people, pets and fish. Contact with, or ingestion of water containing these toxins can be detrimental for humans and animals. Health issues can include skin irritation, gastrointestinal problems, and liver damage. 

• Dead zones in lakes. When cyanobacteria blooms die off, they use up available oxygen during decomposition. This causes oxygen deprived dead zones in water bodies where aquatic life can not be supported.

• Economic impacts caused by cyanobacteria blooms may include declines in tourism and recreation opportunities, reductions in property values and increases in costs associated with drinking water safety.

Cyanobacteria play an important role in ecosystem function, but when factors cause their excessive and rapid growth, it can have harmful consequences for all lake users. To mitigate the impacts of excessive blooms, we must tackle the causes by managing water resources effectively. Lowering nutrient pollution, early detection of blooms, and public education is a great start to safeguarding our lake and the health of lake users. 

Although uncommon in Lake Windermere, please report suspected cyanobacteria blooms for immediate sampling by calling our office at (250) 341 6898. Alternatively, contact your local health authority. For further information on our programs and how to get involved visit our website at [email protected]