14 February 2019
Toxic algae in the Waingawa and Otaki rivers are at extreme levels of more than 50% riverbed cover. Detached mats of dried algae are widespread along the river margins. Mats have also been found in the Waikanae River at Jim Cooke Park.
The algae is shiny brown/dark green and coats submerged riverstones. When it dies it floats to the surface and forms brown mats at the water’s edge. It is important to keep an eye on babies and toddlers who are inclined to put objects in their mouths. Seek emergency medical attention if anyone in your group swallows toxic algae.
Contact with toxic algae can cause symptoms such as skin irritation, nausea, vomiting, numbness, tingling or muscle twitches. You may feel short of breath. If you develop these symptoms following contact with the river, please contact your doctor or Healthline on 0800 611 116. Swallowing toxic algae has the potential to cause serious health issues such as convulsions or loss of consciousness, symptoms which need urgent medical attention.
This is the first time guideline levels have been exceeded in Otaki River. The affected area extends from Hautere all the way down to the river mouth. The stretch of the river below SH1 is particularly bad. Swimmers should avoid this reach as the risk is very high.
Swimmers should also avoid the Waingawa River.
Caution is also advised when choosing a swimming spot in the Waikanae River downstream of SH1, due to the presence of detached mats.
Keep dogs on leashes in these areas. Dogs are at greatest risk from toxic algae because they love the smell of it and will eat it if they can. During a bloom, they must be kept on a leash along the river bank. If you suspect your dog has eaten toxic algae (even if only a coin-sized amount) take it straight to the vet.
Current toxic algae status
Waingawa River – red flag warning: Toxic algae in the Waingawa River is at extreme levels of more than 50% of riverbed cover. Detached mats of dried algae are widespread.
Kapiti Coast – red flag warning: Toxic algae in the Otaki River is at extreme levels of more than 50% of riverbed cover. Detached mats of dried algae are widespread. Mats have also been found in the Waikanae River at Jim Cooke Park.
Pakuratahi River – red flag warning: the algal bloom in the Pakuratahi River remains just over guideline levels.
Ruamahanga: Toxic algae riverbed cover in the main-stem of the Ruamahanga River remains low. Algal levels in the Waipoua River are also low, no warning.
Hutt River: No warning
Waipapa Stream: Significant algal blooms. Dog walkers should be careful.
Hape Stream: Significant algal blooms. Dog walkers should be careful.
Henley Lake: The toxic algae that grows in Lake Henley is referred to scientifically as “planktonic cyanobacteria”. The toxic algae that grows in our rivers in called “benthic cyanobacteria”. Planktonic cyanobacteria floats freely in the water column (looks a bit like green pea soup) while benthic cyanobacteria grows on the rocks in the river (see attached photo). Please refer to this link for more information regarding the two different cyanobacteria types: http://www.gw.govt.nz/toxic-algae-faqs/