People should continue to take care when walking their dogs
near Otago waterways as potentially toxic algae could be
present on banks as well as in the water after recent high
rainfall, the Otago Regional Council says.
Last month, a potentially toxic cyanobacteria algae formed at
the outlet of the lower Tomahawk Lagoon in Dunedin and
Phormidium, a toxic algae potentially fatal to dogs, was
found in the Manuherikia River at Ophir bridge and upstream
at Booths Rd, prompting the Otago Regional Council to put up
warning signs in both areas.
Otago Regional Council water resource scientist Dr Dean Olsen
said this week the council was continuing to monitor both
Signs remained up at Tomahawk Lagoon as there were concerns
the northeasterly weather pattern which drove the
cyanobacteria to the bottom lagoon and down the outlet to the
beach last month could return.
The algae could produce toxins which might cause skin
reactions in people and dogs.
However, the top lagoon, which most people used, was fine and
had not had a recurrence of the algal bloom that affected it
late last year, he said.
On the Manuherikia River, the algae formed mats attaching to
its bed, but could peel off and wash downstream, which was
when dogs were most at risk.
''So, we've kept the warning signs up.''
The council would reassess the signage if a decent flush went
through the river, although if mats were washed on to the
bank they could still be toxic, Dr Olsen said.
''Anywhere in Otago, people need to be mindful of algae,
especially if rivers have been low for some period.''
The council could not monitor every river in Otago for when a
bloom occurred, so dog owners had to keep an eye out for
''They need to be cautious.''
Lake Waihola had recovered from its algal bloom last year and
continued to return low results for the bacteria.