Algal bloom at Rotokawau Virginia Lake


30 April 2018

Whanganui District Council says an unsightly algal bloom evident at Rotokawau Virginia Lake is likely to resolve naturally as we move into the winter season.

Chief Executive Kym Fell says the Council has been contacted by several residents wanting to know why the heavy green algae is present and what can be done about it. 

Mr Fell says, “Algal blooms are increasingly common throughout New Zealand, especially during the warmer seasons. We expect the algae that has accumulated at Rotokawau Virginia Lake this year is likely to disappear with cooler weather and lower light levels, along with more rain which will help to flush out the lake area.

“The algae has been tested and so far has proved to be a type called Microcystis wesenbergii. It is quite buoyant so in calm conditions it easily forms thick surface scum which looks unpleasant and can smell bad near the lake edge." 

Mr Fell says, “Fortunately this particular type of algae is non-toxic. In the past we’ve had Cyanobacteria, or blue-green algae in the lake – which can be toxic and has a very pungent smell, but so far we’re not seeing that type." 

Whanganui District Council has previously submerged ultrasonic units in the lake which can be effective in breaking down algae, but Mr Fell says the current units are not functioning properly and will soon be replaced.   

“We are doing everything we can, but ultimately we are dealing with a natural process, which is exacerbated by warmer temperatures. It happens every year at Rotokawau Virginia Lake and throughout the country.”


Page reviewed: 01 May 2018 11:00am