Municipal Affairs and Environment

Blue-Green Algae: Frequently Asked Questions

General Information

  1. What are blue-green algae?
  2. What are blue-green algae blooms?
  3. What are the concerns associated with blue-green algae?
  4. When do blue-green algae blooms occur?
  5. Where do blue-green algae blooms occur?
  6. Where do the nutrients come from?
  7. How long will a blue-green algae bloom last?
  8. Why do blue-green algae blooms occur?
  9. Why do blue-green algae blooms sometimes appear over night?
  10. Are blue-green algae blooms predictable?
  11. Can blue-green algae blooms be controlled?
  12. What can we do about blue-green algae blooms?
  13. Are blue-green algae blooms a new problem?
  14. Has there ever been a blue-green algal bloom in Newfoundland and Labrador?
  15. What is the government of Newfoundland and Labrador doing to monitor blue-green algae blooms?

1. What are blue-green algae?

Blue-green algae, more appropriately referred to as ‘cyanobacteria', are plant-like bacteria that most commonly live in fresh and salt water. They are often blue-green in colour but they can also range from olive-green to brown to red. Like algae, they are photosynthetic, capable of converting sunlight and nutrients into the energy required for growth and reproduction. Blue-green algae are usually small and unicellular, but can grow or accumulate in concentrations that are large enough to see.

Anabaena spp, Paddy's Pond

Anabaena spp, Paddy's Pond

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2. What are blue-green algae blooms?

When conditions are favorable, blue-green algae can grow profusely and make pond or lake water look like ‘pea soup'. This condition is called a blue-green algae bloom.

Anabaena spp, Paddy's Pond

Blue-green algae bloom Paddy's Pond, 2007

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3. What are the concerns associated with blue-green algae?

Concerns associated with blue-green algae include discolored and cloudy water, taste and odour problems, depletion of oxygen and toxin production. Some blue-green algae species produce toxic compounds inside their cells. Some of these toxins can affect the liver (hepatotoxins) or the nervous system (neurotoxins); others can irritate the skin (dermatotoxins). The most common of these globally are the hepatotoxins known as microcystins. Toxins are not produced during all blue-green algae blooms and there is no easy way to tell when or if a bloom is producing toxins. The only way to be sure is to have water samples analyzed in a laboratory.

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4. When do blue-green algae blooms occur?

The main factors which appear to determine the development of blue-green algae blooms are light, temperature, and nutrient concentrations, particularly nitrogen and phosphorus. Blooms are more likely to develop in warm, shallow, slow-moving water, but they may also be present below the surface in deeper, cooler water.

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5. Where do blue-green algae blooms occur?

The main factors which appear to determine the development of blue-green algae blooms are light, temperature, and nutrient concentrations, particularly nitrogen and phosphorus. Blooms are more likely to develop in warm, shallow, slow-moving water, but they may also be present below the surface in deeper, cooler water.

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6. Where do the nutrients come from?

Although blooms of blue-green algae are a naturally occurring phenomenon, human activities can provide the physical and chemical conditions blue-green algae need to thrive. Storm water runoff, industrial effluent, agricultural runoff and effluent from waste management systems including faulty septic systems can lead to the nutrient enrichment of water bodies and promote the occurrence of blooms.

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7. How long will a blue-green algae bloom last?

Blue-green algae blooms can persist for several weeks, and can occur more than once per year.

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8. Why do blue-green algae blooms occur?

Blue-green algae are well adapted to growth and persistence in nutrient-rich lakes, reservoirs and ponds. They can out-compete other algae for optimal levels of sunlight and nutrients, in part, by regulating their buoyancy in the water. Blue-green algae cells have the ability to form gas-filled cavities, which enable them to move vertically through the water column to access optimal levels of light and nutrients. They also use their buoyancy to counter the downward drag of wind currents. The cells can become over-buoyant and concentrate near the water's surface when calm conditions follow windy periods. These surface accumulations intensify if waves carry the blue-green algae along the shorelines and beaches. The results are blue-green algae blooms that make the water look like pea soup.

Anabaena spp, Paddy's Pond

Blue-green algae bloom, Paddy's Pond

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9. Why do blue-green algae blooms sometimes appear over night?

Even if you can't see blue-green algae floating on the surface of the water in the daytime, that doesn't mean they aren't there. Blue-green algae can be suspended at various depths in the water, and their location depends on a number of factors. The most important of these are light and nutrients (phosphorus and nitrogen). Many species of blue-green algae have evolved to be able to control their buoyancy as the availability of light and nutrients change with the time of day and local weather conditions. At night, when there is no light, cells are unable to adjust their buoyancy and often float to the surface, forming a surface bloom. Thus, this bloom can literally appear overnight and may linger until wind and waves scatter the cells throughout the water body.

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10. Are blue-green algae blooms predictable?

The timing, intensity and duration of a blue-green algae bloom will vary from year to year based on nutrient availability, air and water temperatures, sunlight and wind velocity. Since these factors vary from year to year, blooms cannot be accurately predicted. Blooms may not occur every year in a particular pond or lake, or they may not develop at the same time or with similar intensity each year. The species responsible for each bloom may also differ.

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11. Can blue-green algae blooms be controlled?

Herbicides and algaecides can be used to kill blue-green algae in fresh water, but this is not advisable because these treatments may break open algae cells and release more toxins into the water. These pesticides may also be toxic to other life forms, including fish and the organisms they eat. The use of pesticides in natural lakes and ponds can create more problems than it solves. The mitigation of blue-green algae blooms is better accomplished through preventive rather than remedial measures. Blooms of blue-green algae may only form when nutrients are readily available and taking steps to reduce or prevent additional sources of these nutrients from entering the water can reduce their occurrence.

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12. What can we do about blue-green algae blooms?

A potential long-term solution to problematic blue-green algae blooms is to reduce the amount of nutrients entering lakes and ponds. The main nutrient sources that can be controlled are sewage effluents, agricultural and lawn care runoff, and industrial effluents.

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13. Are blue-green algae blooms a new problem?

Research suggests that blue-green algae have been around for millions of years. Scientists have recorded blue-green algae blooms dating back to the 12th century and they have documented the toxic effects to livestock for more than 100 years. However, it is likely that the frequency and duration of blooms are increasing as a result of increased nutrient concentrations and climate change.

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14. Has there ever been a blue-green algal bloom in Newfoundland and Labrador?

The first confirmed blue-green algae bloom in Newfoundland and Labrador occurred in mid-August 2007 and persisted until early October. Documentation of confirmed blue-green algae blooms can be found in our reports section.

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15. What is the government of Newfoundland and Labrador doing to monitor blue-green algae blooms?

The provincial Department of Environment and Climate Change monitors blue-green algae blooms in fresh water bodies that are of concern to the public. For more information on blue-green algae blooms, visit Health Canada's website Opens in new window.

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