The mercury will be hitting 30degC today, but Pegasus residents won't be able to cool off in the subdivision's lake because of toxic algae.
The Canterbury District Health Board has issued a health warning after potentially toxic blue-green algae (planktonic cyanobacteria) was found in the man-made lake, north of Canterbury.
People and animals, particularly dogs, should avoid contact with the water until the health warning has been lifted.
"Exposure may cause skin rashes, nausea, stomach cramps, tingling and numbness around the mouth and fingertips," Canterbury Medical Officer of Health Dr Ramon Pink 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."
No one should drink the water from the lake at any time, even after boiling as it still doesn't 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."
The Waimakariri District Council, Pegasus Resident's Association and Todd Property – the current 'owners' of the lake – met at the start of the week to address the issues.
Among concerns was the amount of weed that also grows in the lake, which the group says is commonly found freshwater lakes.
Facts about cyanobacteria: