An old mine shaft has been confirmed by the Waikato Regional Council as the cause of the Ohinemuri River turning “bright orange”.
The discolouration, which appeared to enter the river downstream of the Waitawheta River, was reported to the council around 3pm yesterday.
Regional compliance manager Patrick Lynch said the sediment appeared to have shifted from an old mining asset in the hills above the Karangahake Gorge car park.
The flow of water coming from the shaft was running relatively clear and appeared to be flowing into “maybe a hand dug, tool dug channel”, he added.
Plumes of sediment can be seen moving through the Ohinemuri River, turning it bright orange. (Source: Pine J Brown) (Source: Supplied)
“There is still sediment that has settled in the river in quiet locations or around rocks, but most of it has been flushed through the system.
“The settled sediment may be present and visible for some time, and we still advise caution as we do not know yet what it contains.”
Council staff have taken more water samples upstream and downstream and have taken more samples of the settled sediment.
Sample results could take up to 10 days.
Lynch said the colour indicates it will be iron-related and that it will be likely to be “highly acidic”.
“So again, we advise people to treat it as contaminated and not touch it.”
Substances that can be found in old mine assets can include arsenic, cadmium, chromium, and antimony, which could cause risk.
“We are testing for these heavy metals, and also mercury, both totals and dissolved.
“We really want to understand how this event happened and that investigation will take time. It’s also one of those situations where we are relying on mother nature – a rain event – to wash the contaminant away. The more water it’s exposed to, the more diluted it will get.”
Lynch said a plane was being flown in a grid pattern to determine if a sediment plume was apparent.
The plume was expected to reach the ocean in the Firth of Thames by 10am today.
Pollution highlights ‘severe mining risks’ – Green Party
The Green Party claimed the severe pollution of the Ohinemuri River caused by an old mining shaft could become a “more common occurrence” under the Government’s proposed mining reforms.
Resources spokesperson Steve Abel said the state of the river paints a picture of what the future looks like if the Government “unleashes mining” across the country.
“The desecration of the Ohinemuri river with waste from an old mining shaft is a stark example of the toxic legacy mining leaves behind. Ruined nature haunts communities long after the jobs have dried up and the profits have been funnelled overseas.
“Meanwhile, the Luxon Government looks set to fast-track a laundry list of mining projects that will throw our natural world into even further disarray. Mining on conservation land and in the areas critically endangered species call home remain on the table.”
He said expanding mining during a climate and biodiversity crisis is “reckless” and will see future generations pay the price for today’s mistakes.
“No one wants a future filled with fluorescent rivers and climate-charged catastrophes. The solutions exist, all that is missing is political will.”