More toxic algae found in the Mataura River

Thursday, 1 April 2021

Toxic algae (cyanobacteria) has been detected in the Mataura River but can occur in any river or lake, often forming dark mats. It's best avoided as it can be toxic to people and fatal to dogs.

More toxic algae has been found in the Mataura River, prompting Environment Southland to warn people not to have contact with the river, or to take their dogs near it.

On Thursday, the regional council issued a press release saying its latest monitoring had found elevated levels of the toxic algae benthic cyanobacteria in the Mataura River.

The latest discovery is near the Mataura Bridge, in Mataura, and this follows confirmations that toxic algae is present at the Riversdale Bridge and Gore areas.

The toxic algae can be recognised at rivers and streams as a green/brown slime on rocks, or dark brown/black mats at the water’s edge. Several factors can contribute to the growth of toxic algae, such as high levels of nutrients, run-off into waterways, a sudden increase in temperature, and low flows.

* Raised e-coli levels in Mataura River

Toxic algae has been found at the bridge at Mataura. It is harmful to people or animals if swallowed.

* Southlanders warned to steer clear of toxic algae sites

These algae can produce toxins that are harmful to people and animals if swallowed, or through contact with skin. People and animals (dogs in particular) should avoid contact with the Mataura River and be mindful of the potential health risks, until health warnings are removed.

If you experience health symptoms after contact with contaminated water, visit a doctor immediately. If you are concerned that any animals have consumed toxic algae or contaminated water, they should be taken to a vet immediately.

In February, the Clutha District Council reported a dog had died from drinking water from drainage ditches along the flood bank near the Clutha River.

Environment Southland science manager Dr Elaine Moriarty said Environment Southland monitors for toxic algae weekly during summer.

“It’s really important that people know what to look for and take a cautious approach to swimming and walking dogs off-lead along rivers as we can’t assess every reach of every river.”

Toxic algal blooms have plagued many lakes and rivers around the country this year, but this is the first confirmed bloom in Southland this summer.

“Last year we alerted people to toxic algae in a number of rivers, but this year, we haven’t had the right conditions for it to bloom. Instead, we’ve had rather unsettled weather and periodic rain, which helps to flush any algae away.”

In addition to weekly summer monitoring, Environment Southland monitors toxic algae monthly during the rest of the year at some river and lake sites across Southland.

More information can be found on Environment Southland’s website www.es.govt.nz/toxic-algae.