Cyanobacteria (Blue-Green Algae)

What is cyanobacteria? 

Cyanobacteria is also known as blue-green algae. However, this harmful “algae” is actually a bacteria. Cyanobacteria are single-cell, microscopic organisms that are naturally occurring. The bacteria are found in all types of water: freshwater, marine water, and brackish waters (combined salt and freshwater). They are found in both warm and cold climates, even as far south and north as the poles. 

When cyanobacteria multiply quickly, they form what are known as blooms. These blooms severely impact the drinking as well as recreational water quality for humans, as well as aquatic life and any animals using the water as a drinking or food source. Cyanobacteria fall into a category called Harmful Algal Blooms, or HABS. 

How does cyanobacteria impact water quality?

Cyanobacteria use sunlight to make their own food. In warm, nutrient-rich environments, cyanobacteria can multiply quickly. Eutrophication means the nutrient-enrichment of water from nutrients, namely nitrogen and phosphorus. Nitrogen and phosphorus make their way into water bodies from urban and agricultural runoff or from the erosion of naturally or artificially fertilized soils. Storm sewer discharges, combined sewer overflows, sewage bypasses, and other discharges of agricultural and industrial wastes are also major contributors to nutrients. Septic systems can also be a significant source of nutrients. 

The mix of sun and nutrients creates blooms that spread across the water’s surface. The blooms can become visible. Some can get so big and bright that they can be seen from space. 

As the bacteria multiplies the blooms can become toxic. Cyanotoxins are the toxins cyanobacteria can produce. These can have very serious health consequences for humans, as well as on the animals living in or near the water. 

How does the quantity of blue-green algae (cyanobacteria) in water samples measure health risks?

Cyanobacteria is identified in waterbodies in two ways: through visual observation or through sampling. Samples require a specialized lab for processing.The concentration of cyanobacteria in a water sample is typically measured as cells per ml.

In Canada, the federal government’s recommended guidelines for quantifying cyanobacteria are the following

Cyanobacteira ∗ 

  • Total cyanobacteria: 50 000 cells/mL
  • Total cyanobacterial biovolume: 4.5 mm3/L
  • Total chlorophyll a: 33 µg/L