Health New Zealand Te Whatu Ora issued the warning on Thursday last week.
Notifiable disease data released on Monday, for the week ending on Friday, showed one case of chemical poisoning from the environment.
National Public Health Service specialist Claire Salter said chemical poisoning included exposure to toxins produced by the cyanobacteria type of algae.
‘‘The reported case was exposed while swimming. There was no warning in place at the time the person swam,’’ Salter said.
‘‘The lake is regularly monitored for the presence of cyanobacteria by Environment Canterbury (ECan). A public health warning was issued after ECan alerted National Public Health Service to the presence of potentially toxic algal bloom in the lake.’’
The toxins can trigger asthma and hayfever symptoms, skin rashes, stomach upsets, and neurological effects such as tingling around the mouth, headaches, breathing difficulties and visual problems. They are also dangerous for dogs.
The symptoms may not appear until sometime after contact with affected water.
Last year a warning about toxic bluegreen algae was prolonged, lasting from January to June.
The district council had hoped a health warning could be avoided this year with new measures including the operation of a $180,000 weed harvester.
While the lake is tested weekly by ECan, cyanobacteria concentrations can change quickly with environmental conditions, for example, wind.
If you feel unwell after swimming in a lake or river, seek advice from your doctor or Healthline on 0800 611 116.
