Toxic algal blooms will be ongoing, says medical officer of health

Toxic algae has become a problem in the South Canterbury catchment.
Rosa Studholme/Stuff
Toxic algae has become a problem in the South Canterbury catchment.

Toxic algae outbreaks in South Canterbury rivers are only going to increase, the region's medical officer of health has warned.

"They're becoming increasingly common over the summer period," Canterbury District Health Board medical officer of health Dr Alistair Humphrey told Stuff.

"It's not just that we're getting better at measuring and monitoring them, there is a genuine increase.

Canterbury medical officer of health Dr Alistair Humphrey, left, says people should expect more toxic algal blooms in the South Canterbury catchment. (File photo)
JOHN KIRK-ANDERSON/STUFF
Canterbury medical officer of health Dr Alistair Humphrey, left, says people should expect more toxic algal blooms in the South Canterbury catchment. (File photo)

"Overall, we are seeing longer seasons for toxic algae. This is something that should concern everyone."

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As of Monday, the Waihi River at Wilson Street footbridge, Geraldine, the Waihao River at Bradshaws Bridge, and three spots on the Opihi River - at State Highway 1, Waipopo Huts and Salesyard Bridge, all had warnings for toxic algae. 

Some of these warnings, such as the Opihi River at State Highway 1, have been in place since the end of November, while the most recent - at Waihi River - was put in place on January 15.

The warnings, issued by Community and Public Health, say humans and animals, particularly dogs, should avoid these areas until the health warning has been lifted. 

Humphrey said exposure to the algal mats may cause skin rashes, nausea, stomach cramps, tingling and numbness around the mouth and fingertips.

Humphrey said there were a number of aggravating factors causing the problem, including climate change, and increased nutrient loading in the region's rivers and streams.

Some of the reasons had been due to years of nutrient loading and the extraction of water, which meant it would take a long time before there would be visible improvements in certain catchments, he said.

"Taking water out of the system, combined with the heat, means there is less opportunity for the toxic algae to be washed away."

Humphrey said the process of improving water quality and addressing climate change required a "bold approach" by the Government, as well as improved behaviour from everyone across the board.

"While there are farm management plans in terms of nutrient runoff, and most farmers adhere to them, they're often not set at a very high bar. We need to raise that bar.

"But the most important thing we can do is adhere to the Paris Accord and do what we can as a country to mitigate climate change.  "

Humphrey said he was concerned about reports of people vandalising the warning signs.

"They're put up for a reason, and anyone who vandalises them is putting others at risk."

Central South Island Fish and Game chief executive Jay Graybill said any outbreak of toxic algae was a concern, especially as it could affect the health of humans and animals.

"We understand it's at its worst during the summer months, when there are warmer temperatures and reduced flows," Graybill said.

Stuff