People and animals, particularly children and dogs, should avoid contact with the water until the health warning has been lifted.
Planktonic cyanobacteria are floating algae suspended in slow moving water such as in a lake. It often produces bright green or blue-green soup-like scums, according to Environment Canterbury.
Canterbury's Medical Officer of Health, Dr Cheryl Brunton, said today the algal bloom can produce toxins harmful to people and animals.
“Exposure may cause skin rashes, nausea, stomach cramps, tingling and numbness around the mouth and fingertips.
"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,” Dr Brunton says.
“No one should drink the water from the lake at any time. Boiling the water does not remove the toxin.”
Lake Pegasus in the Waimakariri District is being monitored on a weekly basis and the public will be advised of any changes in water quality.
