Holes in wall designed to keep polluted water out of Lake Rotoiti alarm locals

RNZ News

8 hours ago

Large holes have formed in the sides of the Ōhau channel diversion wall, which was constructed to block the flow of more polluted water into Lake Rotoiti.
Photo:
Supplied
There is growing discontent in Rotorua about the state of the Ōhau channel diversion wall, which was meant to protect the pristine waters of Lake Rotoiti.
The wall was built in 2008 to divert polluted nutrient-rich water from Lake Rotorua, which otherwise flowed into Lake Rotoiti through a small channel.
But the wall is corroding, and locals RNZ spoke to said the Bay of Plenty Regional Council wasn't fixing it fast enough, something the council disputed.
Lake Rotoiti is one of the larger lakes in the region, and also one of the most popular.
Lakes Water Quality Society chairman John Gifford said the Ōhau diversion wall was expected to last 50 years, but only six years after it went in, corrosion was noticed.
Now large holes had opened up, and instead of a diversion wall it was more like a leaky bucket.
Lakes Water Quality Society chairman John Gifford, at Lake Rotoiti.
Photo:
RNZ/ Libby Kirkby-McLeod
"With holes in the wall of course there's the opportunity for water to move straight through the wall, contaminate and increase the nutrient-load of Lake Rotoiti and that's just totally inappropriate," Gifford said.
However, Bay of Plenty Regional Council lakes operations manager Andy Bruere said it wasn't as bad as it sounded.
"The wall is still there. Having some holes in it doesn't mean it's not doing its function," Bruere said.
"It's continuing to function, but probably not quite as efficiently as it would if it had no holes in the wall."
Lake Rotoiti
Photo:
RNZ/ Libby Kirkby-McLeod
Bruere said that when the wall went in, the water quality of Lake Rotorua was very bad, but that wasn't so much the case now.
"It's important to acknowledge that we have made very significant improvements to the water quality in Lake Rotorua and so that makes a difference to the impact of the wall, compared to 2008 when it was put in."
This argument isn't very convincing though to locals such as Tim Manning, who wasn't happy with the regional council.
"Its job is to keep the diversion going for 50 years and its mandate is environmental. It made me think maybe [Minister for Regional Development] Shane Jones got it right that these regional councils are
so far out of touch
they maybe shouldn't be there," he said.
Manning had lived on Lake Rotoiti for 35 years, and also owned the local hot pools.
He said the lake was awful before the diversion wall went in.
"There was algal blooms, there was discoloured water, there was smells, there were people being sick," he said.
One of the holes in the wall, underwater.
Photo:
Supplied
The difference after the Ōhau diversion wall went in was stunning - for a time.
"The last five or six years, every year, it goes backwards.
"It's discolouring more, there's more algal blooms cropping up - not quite to the extent it got to 15 years ago - but every year it's getting worse," he said.
Both John Gifford and Tim Manning said the regional council was not doing enough to stop Lake Rotoiti from becoming polluted again.
But Andy Bruere said that wasn't the case.
"We have a strategy around managing the wall which we put in place in 2015, so we are monitoring the corrosion every three years and that is very intensive and detailed monitoring," he said.
Bruere pointed out that the council put in a beam to strengthen the wall and was trailing ways to repair the holes.
"And then also we are currently looking at a range of options around what could be done to repair the holes and repair the wall in a short-term way or in a long-term way."
He said that it was important that any improvements had a positive effect, and the council also needed to consider the level of impact climate change might have in the future.
Whether this will satisfy unhappy locals was still to be seen.
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