Toxic algae has been found in three more locations Southland.
Environment Southland said latest monitoring has picked up elevated levels of the algae in the Waikaia River at Waikaia, the Mataura River at Mataura Island Bridge and the Whitestone River downstream from Manapouri-Hillside.
Earlier this week, it advised that Aparima River at Otautau has been affected and active warnings were already in place at the Waikaia River at Mahers Beach, the Hamilton Burn at Affleck Road, and the Waiau River near Excelsior Creek.
River users and animals should avoid contact with algal mats and remain alert in other parts of these rivers for algal growth or mats of algae floating in the water, it said.
Toxic algae (benthic cyanobacteria) can be recognised at rivers and streams as a 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 and animals (dogs in particular) should avoid contact with the river and be mindful of the potential health risks, until health warnings are removed."
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, it advised.
"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 addition to weekly summer monitoring, Environment Southland monitors toxic algae monthly during the rest of the year at a number of river and lake sites across the region.
