Swift action on algae bloom praised

Otago Daily Times

24-06-2025

The Gore wastewater treatment plant was affected by an algae bloom in early March. PHOTOS: AME MCSPORRAN/GDC
Decisive action by Gore District Council staff turned a potentially disastrous algae bloom into a cause for celebration.
Although algae blooms are a normal occurrence, the extreme expansion at the water treatment ponds in Gore was anything but.
In the council report, Three Waters operational manager Aaron Green described the bloom which broke out on February 21-22 and how the discharge to the Mataura River was disconnected.
Levels took off far quicker than anyone could predict, he said.
Blooms could be a pesky situation to deal with, releasing toxins into the water, and causing environmental changes which could lead to noncompliance with resource consent law, the report said.
Council staff moved quickly to engage shareholders in the treatment plant, and the decision was made to use Earthtec, a water treatment chemical.
Earthtec was the most expensive option for products, but meant less was used overall, and was a success.
Both ponds were treated, with pond one showing a 48% reduction in total suspended solids (TTS), with pond two requiring another dose to dip to acceptable levels.
Quick action led to it being mainly clear a month later.
In addition to this, the use of Earthtec did not increase the concentration of toxins in the pool which can be released if algae die, as they simply sunk to the bottom inert.
A presentation detailing the event and the steps taken was delivered to the council's audit and risk committee meeting in Gore yesterday.
Councillors and staff in attendance were appreciative of the work of Mr Green and his team.
Mayor Ben Bell said the incident was quickly handled by the team, before a potential crisis emerged.
"I'm always a fan of issues that come to me as non-issues since they are dealt with so well."
The ponds will be monitored regularly to catch aberrant blooms before they hit, although it is unknown exactly why this one was so severe.
Temperature was thought to be the main condition for algae growth, but climate research has shown outbreaks can occur at 10°C.
Suspended solids in water, pH levels, water, temperature, all can contribute to an outbreak.