Health Warning - Toxic blue-green algae in Lake Pegasus

Thursday February 12, 2015

The Community and Public Health division of Canterbury District Health Board has issued a health warning  after potentially toxic blue-green algae (planktonic cyanobacteria) was found in Lake Pegasus.

People and animals, particularly dogs, should avoid contact with Lake Pegasus until the health warning has been lifted.

Dr Alistair Humphrey, Canterbury Medical Officer of Health, says the algal bloom can produce toxins harmful to humans and animals.

"Exposure may cause skin rashes, nausea, stomach cramps, tingling and numbness around the mouth and fingertips," Dr Humphrey says.

"If you experience any of these symptoms visit your doctor immediately and please let your doctor know if you have had contact with the lake water."

He says boiling the water does not remove the toxin.

"No one should drink the water from the lake at any time."

Environment Canterbury will monitor this bloom on a weekly basis and the public will be advised of any changes that are of public health significance.

Facts about cyanobacteria:

  • The algae occur naturally but can increase rapidly during warmer months.
  • If the water is cloudy, discoloured, or has small globules suspended in it, avoid all contact.
  • Not all cyanobacterial blooms are visible to the naked eye and toxins can persist after the blooms disappear.
  • Cyanobacterial concentrations can change quickly with changing environmental conditions (e.g. wind). If a health warning is in place avoid contact with the water.‚Äč

For further information visit

Or contact Community and Public Health on (03) 364 1777.


Page last reviewed: 13 February 2015