Context: Toxins made by microscopic algae in water caused the previously unexplained deaths of hundreds of elephants in Botswana, wildlife officials say.

Two elephants lie beside a watering hole


  • Botswana is home to a third of Africa's declining elephant population.

What are cyanobacteria?

  • Scientists warn that climate change may be making these incidents - known as toxic blooms - more likely, because they favour warm water.
  • Cyanobacteria, also known as blue-green algae, are found worldwide especially in calm, nutrient-rich waters.
  • Some species of cyanobacteria produce toxins that affect animals and humans.
  • People may be exposed to cyanobacterial toxins by drinking or bathing in contaminated water.

Oscillatoria, genus cyanobacterium, blue-green algae, seen under a microscope.

  • Cyanobacteria are aquatic and photosynthetic, that is, they live in the water, and can manufacture their own food. 
  • Because they are bacteria, they are quite small and usually unicellular, though they often grow in colonies large enough to see. 
  • Cyanobacteria have the distinction of being the oldest known fossils, more than 3.5 billion years old.
  • Many Proterozoic oil deposits are attributed to the activity of cyanobacteria. 
  • They are also important providers of nitrogen fertilizer in the cultivation of rice and beans. 
  • The cyanobacteria have also been tremendously important in shaping the course of evolution and ecological change throughout earth's history, as the oxygen atmosphere that we depend on was generated by numerous cyanobacteria during the Archaean and Proterozoic Eras. 
  • The other great contribution of the cyanobacteria is the origin of plants. 
  • The chloroplast with which plants make food for themselves is actually a cyanobacterium living within the plant's cells.