The local Medical Officer of Health has issued a health warning for Lakes Ohakuri and Maraetai, two of the Waikato River hydro lakes.

These have both returned laboratory results showing high concentrations of cyanobacteria, or blue-green algae, following regular water sampling by Waikato Regional Council and in collaboration with Ngāti Tūwharetoa Iwi. 

“It is important to avoid any recreational activity which results in significant contact with the water in these two lakes,” Dr Phil Shoemack, Medical Officer of Health with the National Public Health Service said.

“Unfortunately, these lakes have had similar algal blooms over recent summers and it is extremely difficult to predict how long the warnings will remain in place.” 

Cyanobacteria can release toxins which may trigger asthma and hayfever symptoms, skin rashes, stomach upsets, and in some cases neurological effects such as tingling around the mouth and fingers, headaches, breathing difficulties and visual problems.  

“Algal mats and scum may also accumulate along the shoreline of the lakes and so it’s especially important that parents ensure that children avoid contact with these as they may be toxic,” said Dr Shoemack.  

Dogs are particularly at risk and should also be kept away from the shoreline. Elsewhere in New Zealand there have been reported deaths of dogs that have eaten algae on shorelines. 

Most algae are harmless, but high levels of some species may be toxic, and blooms may result in health warnings being issued. Photo/Waikato Regional Council.

Before heading to rivers and lakes, people are encouraged to look out for health warnings from www.lawa.org.nz, and to keep an eye out for signage at recreational water locations.  However, even if no official warning is in place, people still need to be cautious before going into the water.  

“Algal blooms are unpredictable and can grow unexpectedly and shift around, especially in lakes” said Dr Shoemack.

“So even if there’s no alert or signage in place, always check first and if the water doesn’t seem right, stay away and stay out.” 

For up-to-date information on health warnings specific to the Bay of Plenty and Lakes districts, visit: https://toiteora.govt.nz/public/health-topics/recreational-water