The Waihōpai River in Invercargill is one of several sites in Southland where harmful algae has been found. (File photo). Photo: LDR / Matthew Rosenberg
A spate of toxic algae appearances in Southland has prompted warnings at rivers across the region.
On Thursday, Environment Southland released an alert that harmful algae had been found at Whitestone River - near Te Anau.
It followed an alert the day before for a section of the Waihōpai River in Invercargill.
Environment Southland senior scientist surface water quality Katie Blakemore said algae was a natural part of a river's ecosystem, but some species were capable of producing toxins.
Problems were more common in summer, especially when there hadn't been much rainfall and river flows were stable.
"We can't answer how long it will be around for. Largely a bloom could continue until we get a rainfall event that changes the flow conditions in the river," she said.
"Flow is probably the most critical factor."
In the meantime, Blakemore was encouraging people to check rivers before swimming or letting their dogs off the leash.
The regional council issued warnings for monitored locations, but conditions could change between visits and not all sites were checked.
Dark green or black algae spelled bad news.
An example of toxic algae on a rock. Blakemore said dark green or black algae are the ones to watch out for. Photo: Supplied / Environment Southland
Blakemore said they asked the public to stay informed and check Environment Southland's website for details of what to look out for.
There are currently three warnings in place for Southland.
Warnings in Fiordland include Whitestone River downstream of Manapouri-Hillside Rd and Waiau River near the Excelsior Creek inflow.
There is one warning for Invercargill's Waihōpai River, upstream of Queens Drive.
Last week, the council also revealed it was investigating reports of an algal bloom in Doubtful Sound, and whether it was connected to an unusual number of fish deaths.
LDR is local body journalism co-funded by RNZ and NZ On Air.
