Canterbury District Health Board is urging people to avoid one of the region's lakes, issuing a health warning over possible toxic algae.
In a statement today, the DHB said potentially toxic blue-green algae, known as planktonic cyanobacteria, was found in Te Roto o Wairewa – Lake Forsyth.
It advised people to avoid the lake, warning that pets - particularly dogs - should not be allowed near the water until the health warning has been lifted as the algae can produce toxins harmful to both humans and animals.
"Exposure may cause skin rashes, nausea, stomach cramps, tingling and numbness around the mouth and fingertips," Canterbury Medical Officer of Health Dr Cheryl Brunton said.
"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."
She said animals showing signs of illness after coming into contact with algal mats or scums should be taken to a vet immediately.
Brunton said no one should drink water from the lake at any time, and that boiling it won't remove the toxin from the algae.
She also urged people to avoid eating fish and shellfish which can concentrate toxins, but if they are consumed people should remove the gut and liver and wash in clean water.