Alarmingly high levels of aluminium found in Northern Wairoa near Dargaville

The Northern Wairoa River, which closely hugs the town of Dargaville, has been found with levels of aluminium so high it is potentially toxic to fish. Photo / Tania Whyte

Voluntary water testing in Northland’s Kaipara Harbour has found alarmingly high levels of aluminium in the Northern Wairoa River near Dargaville.

The results - more than 30 times the freshwater standards - show a need for more testing to better understand what is happening.

The tests were done by Grant Hoey from Cannalytic Profiling, a company which regularly tests water around the country.

Now based in Auckland, Hoey heard about “zombie fish” - snapper so sick they are barely alive - being fished up near Dargaville.

“I grew up in Dargaville and I know the place quite intimately ... I was up there and did a couple of samples in a couple of spots.”

Using a mass spectrometer, which tests heavy metals in the environment, water at Ruawai wharf tested normal, but Dargaville wharf and Tirarau St both showed high levels of aluminium - 3.25mg/L and 1.77mg/L respectively.

These results are 59 times and 32 times the freshwater and marine guidelines by the Australia and New Zealand Environment and Conservation Council, which says aluminium should be less than 0.055mg/L for the health of aquatic plants and animals.

Both results are also breach the 2022 New Zealand Drinking Water Standards, of less than 1mg/L, which includes a safety margin for humans.

Hoey said the results show a need to do further testing, including of tributaries, and he is working with Dargaville Ratepayers and Residents’ Association to map the best spots and get samples.

Experts agree more testing is needed, with the aluminium potentially coming from natural sources like silt and clay particles, or chemical use - with aluminium products sometimes used in water treatment and earthwork sediment ponds.

Ratepayers and Residents Association’ chairwoman Rose Dixon said the results are alarmingly and worryingly high.

“We understand that aluminium at these concentrations is known to be toxic to aquatic life, especially fish.

Dargaville Ratepayers and Residents' Association chairwoman Rose Dixon, with vice-chairs Sam Erickson and Jo Floyd in front of the Northern Wairoa River, says the high aluminium is a concern.

“While Ruawai’s results were normal, this contrast suggests Dargaville as the potential source.”

Dixon is concerned about the impact on people, either from swimming in the river or eating fish caught there.

The group previously called for a government inquiry into the high levels of pollutants in the Northern Wairoa River, which could be contributing to the illness in snapper.

Levels potentially toxic for fish, council says

Northland Regional Council said the level of aluminium reported could be considered high and “potentially toxic” for fish and other aquatic creatures, a spokesperson said.

Further investigation is needed, both to quantify any potential risks and to identify potential causes.

The council’s proposed regional plan uses the Australasian guidelines, of aluminium less than 0.055mg/L, as the standard for protecting 95% of species in rivers.

But the council does not regularly test for aluminium in any of the water quality tests it runs.

There is still bird life on the banks of the Northern Wairoa River in Dargaville but the high levels of aluminium could be potentially toxic to marine life. Photo / Michael Cunningham

“Aluminium is not a typical water quality concern for the council due to Northland’s predominantly rural landscape. Aluminium discharges are typically associated with a consented industrial activity in a more urban environment,” the spokesperson said.

The tests the council does do shows poor water quality in the Northern Wairoa, with its tributaries showing problems with sediment, phosphorus, E. coli and poor ecosystem health indicated by a lack of stream invertebrates.

On top of this, both Dargaville and Te Kopuru wastewater treatment plants were compliant only about half the time in the past 12 months, with breaches for minor to moderate reasons.

In Dargaville, the non-compliance related to the levels of suspended solids in treated wastewater discharged into the river. In Te Kopuru, it related to the levels of E. coli, suspended solids and ammonia in discharges.

The council has no current concerns about leachate from the Dargaville landfill at Awakino Rd, with annual monitoring done for ammonia and some heavy metals, although not aluminium.

E. coli bigger health concern - health officer says

Health NZ Medical Officer of Health Dr David Sinclair said the levels of aluminium detected in the river are not considered to be a public health risk at this time, as people are commonly exposed to aluminium in their daily lives, such as through antacids.

A bigger public health concern is the level of bacteria, such as E. coli, in the water, which can cause gastroenteritis and skin and eye infections, and affect aquatic plants and animals in the food chain.

Swimming and food gathering in the river at these locations therefore isn’t recommended, he said.

Dixon said this warning begs the question why there hasn’t been any warnings in recent years, to her knowledge, to not swim or collect shellfish from the Northern Wairoa River due to its pollution.

“This has been an ongoing issue for many years. It’s a fact the river has high faecal coliforms and that it exceeded almost all parameters with regards to water quality.”

Denise Piper is a news reporter for the Northern Advocate, focusing on health and business. She has more than 20 years in journalism and is passionate about covering stories that make a difference.