Water warnings issued on Southland rivers as cyanobacteria levels rise
Environment Southland has issued warning notices for three rivers after they were found to contain an increased amount of toxic algae.
Monitoring carried out by the regional council has shown an increase of the benthic cyanobacteria in several rivers, the latest being the Mataura River at Gore.
Last week, higher levels of cyanobacteria was found in reaches of the Hamilton Burn around Affleck Rd and the Upukerora River around the Te Anau-Milford Rd.
The algae can produce toxins that are harmful to animals and humans when eaten or even licked, or when water containing the toxins is swallowed.
* Toxic algae found in Southland river
Council freshwater and marine science leader Nick Ward said there were about 30 monitoring sites throughout Southland that were checked on a monthly basis.
The Mataura River exceeded the 20 percent threshold at monitoring sites in both Gore and Mataura and so the regional council issued a notification to Public Health South and the local councils.
Cyanobacteria was dark green to black in colour and would accumulate in dense mats in rivers where it was rocky.
When bacteria levels reached a 50 percent threshold monitoring would be carried out more regularly than on a monthly basis, Ward said.
There was no way ES could monitor the whole of Southland so it was important people get a sense for what the algae looked and where to find it, he said.
The algae flourished in warm weather and when rivers were in a low flow, Ward said.
When there were high flow events in waterways the algae was usually flushed away, but never completely, he said.
Sometimes people would get it confused with didymo, which had a snot like appearance, Ward said.
"We need to tell people if that risk is there."
Dogs were particularly susceptible to poisoning from both mat-forming and free-floating cyanobacteria as they enjoy being in the water and can consume these algae intentionally or by accident, Ward said
The algae mats could slip off the rock and accumulate on the river banks where dogs could get to easily, he said.
Public Health South medical officer of health Dr Derek Bell said exposure to cyanobacteria might cause symptoms such as skin rashes, nausea, tummy upset and tingling and numbness around the mouth or tips of fingers
Anyone who experienced health symptoms after contact with contaminated water should visit a doctor immediately, Bell said.
Animals that consume cyanobacteria should be taken to a vet immediately.