Weekly monitoring of water quality in Waikato lakes and rivers popular with recreational users has kicked off for the summer season.

The annual Waikato Regional Council programme involves collecting and testing freshwater samples for levels of E. coli and cyanobacteria. E. coli provides an estimate of faecal contamination, while cyanobacteria (blue-green algae) can produce toxins harmful to people and animals.

Council staff, assisted by two summer student workers, has started weekly monitoring this week – at Lake Taupō and four other lakes (Puketirini, Kainui, Rotokauri, Ngāroto), the Waikato River, from Hamilton up to Tuakau, and other rivers in the region, including Kauaeranga, Waihou, and Waipā – with the work continuing to the end of February. Monthly monitoring of the hydro lakes – Karāpiro, Maraetai and Ohakuri – started in November and runs monthly through to April.

Water monitoring data will be available on the Land Air Water Aotearoa (LAWA) website – lawa.org.nz/explore-data/swimming – the day after its collection.

Waikato Regional Council Water Scientist, Dr Mafalda Baptista, says many of our freshwater sites graded poorly for E. coli.

“As a rule of thumb, you should avoid swimming near potential sources of contamination such as flocks of birds, stormwater or wastewater outlets. Avoid swimming for at least 2 to 3 days after heavy or prolonged rain, even for sites that have good water quality,” says Dr Baptista.

Algae occur naturally in our rivers, lakes and streams, and flourish during hot and fine conditions.

“Most algae are harmless, but cyanobacteria may be toxic and blooms may result in health warnings being issued.

“El Niño this summer will translate to warmer growing conditions in our lakes and rivers, and we are likely to see more occurrences of algal blooms.

“We encourage recreational water users to keep an eye on the LAWA website for the latest water quality data. However, algae can accumulate rapidly, despite it being clear the last time we sampled. So, we also encourage water users to use their own judgment before getting into the water.

“If you see water that is bright green like pea soup, then it is safer to stay out.”

Dr Baptista says extra care should be taken with toddlers and dogs as they like to put things into their mouths and even a small amount of cyanobacteria the size of a coin can be enough to cause serious harm if eaten.

Waikato Regional Council works closely with district councils and Te Whatu Ora – Health New Zealand to identify any results that may have public health implications and then communicate them.

Te Whatu Ora Waikato Medical Officer of Health Dr Richard Wall recommends that where health warnings are in place, waterways should not be used for any activity that involves contact with the affected water.

“If people still choose to use the lakes when warnings are in place, or any other lake where there are visible changes to water colour, they should shower and change their clothing as soon as possible afterwards, even if no symptoms are noticeable,” says Dr Wall. “Scums are a particular risk and contact with them should be avoided.”

Dr Baptista says last summer’s trial of a handheld device that measures cyanobacteria pigments produced promising results leading to the extension of the trial in more lakes this summer.

“The device measures the pigment phycocyanin, which indicates the presence of cyanobacteria. By comparing the pigment data with lab results of cyanobacteria, we are able to determine if a cyanobacteria bloom is likely to happen, saving time and enabling better public advice,” says Dr Baptista.

Waikato Regional Council’s summer coastal monitoring programme – which takes in popular Waikato beaches and estuaries – started last month and runs until 31 March.

Land Air Water Aotearoa: lawa.org.nz/explore-data/swimming

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