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Update, August 5: Since the paper went to press last Friday, an oyster farmer has advised that further water testing has been done. The tests again found norovirus present and oyster farms on the Mahurangi River will now remain closed at least until August 26, he says.
The continued and unmonitored release of untreated toilet waste into the Mahurangi River is the likely source of the highly infectious norovirus, which was found in the Mahurangi Harbour on Thursday July 25.
As a result, all Mahurangi oyster farms, which were already closed as a precaution due to earlier heavy rainfall, had the closure extended for a further 28 days.
Food Safety acting deputy director-general Jenny Bishop says commercial shellfish and the water they grow in are subject to strict monitoring testing to ensure that they are safe to eat before they can be harvested and sold.
Nine cases of norovirus have been found in the Mahurangi River in the last 18 months, and the latest positive test is yet another blow for local oyster growers who say deteriorating river water quality, and sewage in particular, is threatening their businesses.
They say that while their operations factor in intermittent closures after heavy rain, the increasing frequency of sewage in the river is the problem
Environmental health scientist Cameron Ormsby, who has been monitoring water quality in the Mahurangi for around 16 years, says oyster farmers are paying the price for Watercare’s lack of investment in wastewater infrastructure. Increased development means that rain, which would have once been absorbed into the soil, is now hitting impermeable surfaces and entering the stormwater system, a system that can’t cope.
While planning is in place to rectify this, the timeframe won’t help oyster farmers who are “getting smashed”. He says there are interim solutions, but Watercare is saying they are either too expensive or not feasible.
“Oysters are filter feeders, which means they are a high risk food,” Ormsby says. “It’s why there has been such a robust testing programme in place for the past 30 to 40 years. But the testing has been based on bacteria, not viruses.
“Contamination from sewage, that’s a whole different kettle of fish. Oysters can filter bacteria in three to four days, but viruses hang around.”
Since testing for norovirus started in 2021, positive results have been recorded in Dyers Creek, Pukapuka Inlet, Cowans Bay, Brownes Bay, Huawai Bay and Te Kapa Inlet.
Ormsby says anyone collecting shellfish recreationally in these areas after heavy rain is potentially at risk.
He says it seems “bonkers” that a multi-million dollar oyster industry is in this position because the regulator (Auckland Council) is showing no interest in holding Watercare to account.
“In other areas, if a water authority was discharging raw sewage into a river, they would be facing massive fines.”
Farmers who Mahurangi Matters spoke to say that they are near breaking point financially. Many had recently renewed their leases with Auckland Council, which had cost some individual farmers close to $100,000.
Matakana Oysters operator Tom Walters, who has worked in the local oyster industry for nearly 30 years and runs a popular retail outlet on Leigh Road, says closures are a fact of life and he normally holds a financial reserve to carry him through these times. However, the lease renewal costs had drained those reserves.
“I’m not set up volume-wise to be a wholesaler and I can’t afford to sit here with my shop closed.
Although our testing regime is world class and transparent, these closures will mean a lot of customers won’t trust our oysters.”
He says the sewage overflows come on top a myriad of challenges, from warmer water to increasing silt loads, and he is seriously considering whether he can continue.
The ‘engineered overflow point’ (a white pipe) located in Elizabeth Street, is a known source of sewage spills. Neighbouring businesses like the Curtain and Blind Specialists report seeing toilet paper in the stream and “a really bad pong” every time there is heavy rain. Manager Carla Kilipati says it is a concern to see school students playing in the creek.
Food Safety says people should not be concerned about shellfish they buy from shops or supermarkets.
However, if anyone gets sick after eating shellfish, they should seek medical help and keep any leftover shellfish in case it can be tested.
Watercare is currently building a new pipeline, pump station, wastewater treatment plant and outfall pipe to cater for growth. As part of these works, it proposes to lay a sewer through the town’s main shopping centre, which many retailers say could be the death knell for their businesses. A decision on the final route is expected in December, but construction of the connection could still be two years away.
