Lake warnings

During the swimming season (Nov–Mar), Environment Canterbury assesses the health risks from faecal contamination (E.coli) and toxic cyanobacteria at popular freshwater swimming sites around the region.

Monitoring of E. coli

Monitoring of the ‘faecal indicator bacteria’ Escherichia coli (E. coli) is vital.  ‘Indicator bacteria’ signal the levels of disease-causing organisms present in the water. It’s important to test for these in water used for recreational activities as they can pose a health risk. The most common illness they cause is gastroenteritis, but respiratory illness and ear/skin infections may also occur.

What is Cyanobacteria? 

Cyanobacteria play an important roll in aquatic ecosystems, but become a problem when they produce toxins which can cause nausea and diarrhoea, and (in extreme cases) more serious health issues for both people and animals.

Routine monitoring 

Routine monitoring for potentially toxic planktonic cyanobacteria is carried out monthly for Te Roto o Wairewa/Lake Forsyth and Te Waihora/Lake Ellesmere. This increases in frequency when potentially toxic planktonic cyanobacteria are identified.

The below health warnings are for planktonic cyanobacteria and faecal contamination (E.coli). 

Lake Forsyth/Wairewa

26 March 2020

Recent water sampling results from Lake Forsyth | Wairewa have indicated excessive levels of cyanobacteria.

A health warning has therefore been issued by Community Public Health. Signs have been erected at the site.

The warning will be in place until a subsequent sample shows cyanobacteria has dropped below the acceptable health risk level.

Eastern Kaiapoi Lake

3rd February 2020

A bloom of potentially toxic blue-green algae (planktonic cyanobacteria) was observed in the Eastern Kaiapoi Lake. 

People and animals, particularly dogs, should avoid all contact with the water.

If you choose to eat fish from waters containing toxic cyanobacteria, you should eat them in moderation. Avoid eating internal organs, such as the liver and kidney of the fish, as this is where accumulation of cyanotoxins may be the greatest. Affected fish may taste earthy. Avoid contact with the water while fishing and wash all fish in clean water.

Lake Rotorua (near Kaikoura)

Last updated 8 March 2019

Long term water testing indicates that there is a regular bloom of the potentially toxic cyanobacteria Anabaena and/or Microcystis present.

There is a permanent health warning advising people to avoid contact with water at this lake.

Environment Canterbury continues to monitor the lake on a regular basis.

Te Waihora/Lake Ellesmere

24 December, 2017 - last updated 8 March 2019

The Community and Public Health division of Canterbury District Health Board has issued a health warning after high concentrations of blue-green algae (planktonic cyanobacteria) were found in Te Waihora/Lake Ellesmere.

People and animals, particularly children and dogs, should avoid contact with the water until the health warning has been lifted.

Environment Canterbury monitors the lake fortnightly and the public will be advised of any changes that are of public health significance.