What's that smell? North Shore residents kicking up stink over sewage overflows

Kaipātiki Stream in Glenfield after a wastewater overflow last week. Photo / Supplied

North Shore residents are kicking up a stink over sewage flowing into a treasured stream, but Watercare lays the blame on "fatbergs" and rags clogging up the system.

Kaipātiki Stream in Glenfield has had eight wastewater overflows in the past year, according to Watercare.

These occurred when there was a blockage in the wastewater pipes - which carry everything that goes into sinks, toilets, showers washing machines and even some industrial waste.

To prevent the sewage backing up into people's homes it is released through manholes and overflow valves. The latest overflows occurred on October 30 and 31.

A resident who frequently runs along the stream contacted the Herald after the latest overflow.

"It has been going on forever. Every time it rains it smells awful."

He said the soil around the stream was black from sewage, and he had even seen toilet paper floating by.

A Glenfield "fatberg" responsible for a wastewater overflow last week. Photo / Supplied

The stream passes through a section of bush for about 400m before it reaches a mangrove-laden inlet and on out into the harbour

The resident said while blockages could explain the major overflows, they didn't explain why there was alway a stench.

However, a Watercare spokeswoman said recent water testing results showed a low presence of ammonia - an indicator of wastewater - suggesting leaks were not an issue.

Sometimes odours could occur naturally in stagnant streams, she said.

In the past year one overflow was caused by a tree falling onto and damaging a pipe bridge, another by a piece of building timber, and the other six all from fatbergs, rags and wet-wipes.

"In each instance, our contractors responded quickly, the blockage was cleared, Auckland Council's Pollution Control team was notified, and the area was thoroughly cleaned," the spokeswoman said.

The Glenfield area has had a particular problem with people and businesses putting cooking fat and rubbish down their drains, she said.

"Fatbergs" occurred when cooking fats and oils hardened in wastewater pipes, and ended up blocking the sewage.

They are not uncommon, with London infamously plagued by "fatbergs" the size of buses.

While Auckland's pipes are much smaller "fatbergs" still pose a major challenge.

"Hot cooking liquids should be poured into containers and disposed of in a rubbish bin- never poured down the sink," the Watercare spokeswoman said.

Another issue was that supermarkets were selling a range of wet wipes that claimed to be flushable.

"It's our view that they're not safe to flush at all," the spokeswoman said.

"They simply don't break down and merge together with fatbergs, creating huge slimy lumps that clog wastewater pipes."

In the next few weeks Watercare would be doing extensive flushing and camera inspections of the local wastewater network to determine if there were further obstructions.

They would also be working with the community on an education campaign around avoiding blockages.

About 70 per cent of blockages in pipes were caused by things going down the drain that shouldn't. Watercare unblocked the system at an annual cost of nearly $1m.

Watercare's message was that only the "three P's" should ever go down the toilet: poo, paper and pee.