Lake about to flip
Scientists say Dudding Lake in Rangitı¯kei may become one of New Zealand’s most polluted lakes – possibly in a few months – if nothing is done.
However, a regional council chairman has said he has seen the lake come right despite being in far worse condition.
Dudding Lake is subject to a public health warning, with people told not to touch the water because of the level of blue-green algae, which can produce toxins harmful to humans and animals, potentially causing skin rashes, nausea and upset stomachs.
At Horizons Regional Council’s environment committee yesterday, natural resources and partnerships manager Dr Jon Roygard said Niwa had been contracted to provide advice.
The lake had an especially high alkaline ph reading in certain areas, and was turbid because of algae in the upper layers. That algae was blocking out sunlight to the plants on the bottom of the lake, known as macrophytes, which needed sunlight to grow. Although those plants were not native, they were better for the health of the lake than having none at all, he said.
The situation was at a point where the lake was at risk of ‘‘flipping’’ – a technical term, Roygard said – from being macrophytedominated to algae-dominated.
The lake could flip in two months, or a few years, he said. The flip could be stopped, but it would be hard work and needed to be sorted sooner rather than later and council staff were working on a plan. But the council’s chairman Bruce Gordon said Rangitı¯kei District Council already had a plan in place. It had released freshwater mussels, and was getting a permit to release carp to assist, he said.
The lake had historical problems with blue-green algae, sometimes much worse than now, but had always righted itself in a few months, he said. ‘‘The advice I’m getting from Rangitı¯kei District Council is ‘back off, we have it covered’.’’
In response, Roygard said the frequency of algae problems was on the rise.
Horizons chief executive Michael Mccartney said it made sense for him to talk to Rangitı¯kei District Council’s chief executive about what was happening, so the two councils could work together to come up with the best option.
Any call about drastic action, such as using chemicals to kill the algae, would require a ‘‘more detailed conversation’’.