The day the Waiwhakaiho ran orange

Kokowai flowing
Aerial photo of the Kokowai Stream high on Mt Taranaki clearly shows the source of the colouration

Taranaki Regional Council inspectorate and scientific staff were mobilised in early November 2013 after reports that the Waiwhakaiho River had turned bright orange in its upper and middle reaches.

In the era of social media and 24/7 internet news coverage, it was clear to the Council that the reports had substance – even before officers arrived on the scene.

But a crime scene it wasn’t. A quick investigative helicopter flight up the river to its headwaters high on Mt Taranaki confirmed what the old hands had already suspected: the culprit was naturally occurring iron oxide.

The source of the discoloration was the Kokowai Stream, a tributary of the Waiwhakaiho River near the Boomerang slip on Mount Taranaki. The name Kokowai means ‘red ochre’.

The entire stream was indeed flowing bright orange when Council officers flew over the area, with a significant rust-coloured flow of water and sediment at the source of the stream.

Subsequent checks revealed a landslip had resulted in pent-up groundwater with high iron levels being suddenly released into the stream.

Iron is a common element in Taranaki’s water and volcanic rock and soils, and rust-coloured deposits or cloudy orange water often occur naturally in Taranaki waterways, though seldom to this extent. The iron reacts with atmospheric oxygen or dissolved oxygen in surface water to form rust-coloured iron oxide which precipitates out and can also give a waterway a cloudy appearance.

Such discoloration is sometimes mistaken as pollution when it is sighted in the lower reaches of waterways. But iron oxide deposits occur naturally and although unsightly, they are not toxic to fish or other aquatic life, and they are not an environmental health risk.

The fast-flowing Waiwhakaiho River cleared quickly. This truly was a one-day wonder, but it gave headline writers an opportunity to exercise their sense of humour in the next morning’s front-page banner: ‘Ore inspiring’.