Source: Waikato District Health Board
Cyanobacterial levels at Lake Ngā Roto have risen to extremely high levels this week, with a consequential increase in health risk to the public. The cyanobacteria biovolume is 123mm3/L compared to the New Zealand guideline level of 1.8mm3/L.
A health warning was issued for Lake Ngā Roto on 8 November 2023. The Te Whatu Ora Waikato Public Health Service is issuing this update to warn people of this significant increase in cyanobacterial levels.
Cyanobacterial bloom at Lake Ngā Roto – image courtesy of Mark Palmer
“We strongly recommend that people avoid any recreational activities that involves contact with the water” says Dr Richard Wall, Medical Officer of Health for Waikato. “People using boats are also advised to stay off the lake, because of the risk of contact with the water”.
The predominant cyanobacterial species present in the lake is a type that is known to produce toxins in New Zealand, which can cause serious illness. The cyanobacterial bloom extends to most parts of the
lake, and is not restricted to the edges of the lake. However, scums may accumulate along the shoreline and are a particular risk as they may contain particularly high levels of toxins.
Cyanobacterial toxins can trigger asthma and hayfever symptoms, can cause skin rashes, stomach upsets, and in some cases neurological effects such as tingling around the mouth, headaches, breathing difficulties and visual problems.
These symptoms may not appear until some time after contact with the affected water. Long-term exposure to cyanobacterial toxins may cause additional health risks.
If contact with water does occur, skin should be rinsed clean and clothing changed as soon as possible.
Dog owners should prevent their dogs from drinking or swimming in the water, as dogs are particularly sensitive to cyanobacteria.
Te Whatu Ora Public Health Unit for Waikato would like to be informed about health problems that develop after exposure to any of the Waikato lakes. Phone Waikato Public Health Service: 07 838 2569.
Lakes Hakanoa, Waikare and Kainui continue to have a cyanobacterial health warning in place.
Up-to-date information on cyanobacterial risk is available by visiting the Land Air Water Aotearoa (LAWA) website at https://www.lawa.org.nz/explore-data/waikato-region/
