“The presence of these bacteria in waterways suggests other pathogens, which are harmful to humans, may also be present,” Hurst said.
Potentially toxic algae include cyanobacteria which appear as black mats on rocks in rivers and green scum in and above water in lakes.
“This algae can be toxic to animals and people.”
Coming into contact with water where the organisms are present in sufficient quantities can lead to conditions such as gastroenteritis, respiratory illness, and ear and skin infections.
An underwater viewer called a bathyscope is used to observe these algae in rivers, while for lakes a sample of water is taken and examined with a microscope.
The Lawa website will be updated when Horizons gets the results for each site so people know which are suitable for swimming.
Lawa’s website holds information on the water quality of swim spots across the country.
Water quality is marked by different-coloured location markers, with green indicating good quality, amber fine quality and red bad quality, based on the most recent test results and the Ministry of Health guidelines.
Hurst said people should always check Lawa for water quality results, but there were other things they should be aware of, especially in and around rivers.
He advised people to stay out of water if it had been raining heavily within the last 72 hours, as it could create faster-flowing water and contribute to higher levels of faecal contamination.
“It is important to check any swim spot before swimming but especially after heavy rain as things may have changed beneath the surface since you were last there,” Hurst said.
“It is especially important to check for large objects.”
Rivers and beaches across Aotearoa could be unpredictable and their power was easy to underestimate, so people should not enter the water alone, actively supervise children and stay out if they were not confident swimmers.
“Also avoid swimming close to cliff faces in case of slips, which can occur any time,” Hurst said.
“Finally, call 111 during any emergency at a waterway.”
Further information about how to stay safe in and around rivers and beaches is available on Water Safety New Zealand’s website www.watersafetynz.org.
