Environment Southland’s (ES) atest monitoring has found high levels of potentially toxic algae in the Mataura River near the Riversdale Bridge and at the Ōreti River at Branxholme.

These alerts are in addition to warnings already in place for the Mataura River at Gore and the Waituna Lagoon.

However ES has now removed the alert for the Mataura River downstream of the Mataura Bridge.

ES advise water users should be vigilant and avoid contact with the algae as similar growth may be occurring in other rivers and tributaries around the region. 

Swimming at these locations should also be avoided.

Algae naturally occur in waterways and can flourish during fine conditions and stable river flows. Most algae are harmless. However, some species can produce toxins and rapidly bloom to high levels. These algae are potentially toxic, and commonly identified in waterways as a dark green/brown slime on rocks, or dark brown/black mats at the water’s edge.

These algae can produce toxins that are harmful to people and animals if swallowed, or through contact with skin. People should keep dogs on a lead and children away from affected areas. Be mindful of the potential health risks, until health warnings are removed.

ES advise fly fishers in the area that it is recommended to:

• wear clothing such as waders to minimise contact with the water.
• wash your hands and any other skin that’s been in contact with the river with clean water and soap. Use of hand sanitiser may not remove all the algae from the skin, so clean, running water is best for washing hands and skin.
• avoid eating the liver and other fish organs, as this is where the accumulation of toxins may be greatest.

Fish caught in water with toxic algal blooms should only be eaten occasionally (less than one meal per week). Fish may taste earthy due to other compounds produced by the toxic algae; there is no relationship with taste and the concentration of toxins.

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.

ES monitors toxic algae monthly during the year at a number of rivers and lakes sites across Southland.

Toxic algae blooms are more likely to occur in summer, but can happen at any time of the year, they say.