Te Whatu Ora Medical Officer of Health for ToiTe Ora, Dr Phil Shoemack, said algal blooms could readily move from one part of the lake to another.
“The algae can also quickly multiply to dangerous levels and lake users need to be vigilant before having any contact with the lake water.
“Algal blooms can sometimes produce toxins that are harmful for people as well as animals. It is best to avoid contact with the water if it looks discoloured, has an unusual smell, has green or brown particles suspended in it, or if you can see scum or leathery mats of algae on the surface or on the bottom of the waterway,” Shoemack said.
He said the toxins could cause “significant ill-health” including affecting the nervous system causing numbness and difficulty with breathing, and also sparking asthma attacks.
“Contact with the water can also cause skin rashes, stomach upsets and visual problems.”
Lakes were typically dominated by free-floating algal blooms, while rivers were prone to algal blooms that grew in mats attached to rocks at the bottom or building up at the shoreline.
Toxic varieties of the blue-green algae can be especially harmful to dogs.
“Algal mats and scum may also accumulate along the edges of lakes or rivers so it’s especially important that parents ensure that children avoid contact with these as they may be toxic,” Shoemack said.
“You should seek medical advice from your GP if you become unwell after having contact with the recreational water.”
Dogs were also particularly at risk of serious illness if they consumed or touched toxic algae, and should be kept away from water with potential blooms and algal mats that accumulate in and around rivers.
A health warning is issued by Toi Te Ora Public Health if recreational water monitoring results from regional councils show a site having high levels of blue-green algae.
Last month, new signs warning lake users of toxic algal blooms were put up around 40 lakeside locations in the Rotorua district as rising outdoor temperatures increase the likelihood of cyanobacteria breakouts.
The Toi Te Ora website said there were active algal bloom health warnings for Lake Ōkaro near Waimungu, Lake Maraetai near Mangakino and Lake Ohakuri near Reporoa. The advice for all was to avoid recreational water contact.
It said some lakes in the Rotorua area – such as Lake Rotoehu, Lake Ōkaro and Lake Rotoiti – were prone to blooms of blue-green algae that may be toxic and harmful to health.
Water at the Ōkere Inlet at Lake Rotoiti was a vivid shade of green in March last year. Photo / Laura Smith
Toi Moana Bay of Plenty Regional Council environmental scientist James Dare said at the time the green water was host to potentially toxic cyanobacteria, dominated by a species called Anabaena circinalis.
