A health warning has been issued after a potentially toxic blue-green algae was found in a North Canterbury lake. People and animals, particularly children and dogs, should avoid contact with Lake Pegasus until the warning has been lifted, a Canterbury District Health Board statement said. Canterbury Medical Officer of Health Dr Alistair Humphrey said the algal bloom could produce harmful neurotoxins. "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." Humphrey said no water from the lake should be consumed as boiling the water would not remove the toxin. "This bloom will be monitored on a weekly basis and the public will be advised of any changes that are of public health significance," he said.