Up the creek: Auckland's dirtiest stream?

John Smith looks over the waters of the Puhinui Stream. Photo / Greg Bowker

A volunteer clean-up at Puhinui Stream, which winds through and under Auckland's south-western suburbs, once pulled "an entire student flat" from its waters.

"A washing machine, a fridge and a couch, all jammed in one corner" says Wai Care co-ordinator Andrew Jenks, who has led replanting and clean-up work there for 10 years.

In a day, volunteers filled two 6x6m skips with junk - tyres, rubbish bags, bikes, whiteware, road signs, shopping trolleys, paper, carpet and plastic food baskets.

As development has intensified in the area in the last 20 years, the 12km stream's middle sections have become a dumping ground. Long-time volunteer John Smith, 80, says the most recent working bee pulled an entire motorbike and car wreck from the stream's banks.

In March last year, a cement spill killed around 500 eels, some of them 50 years old. It was a "heartbreaking" moment for volunteers, many of whom work tirelessly to prevent the waterway becoming a wasteland.

Aucklanders orientate themselves through the road network. From above, motorways, not rivers, are the most distinctive shapes. But 10,000km of narrow streams - nearly all less than 2 metres wide - wend behind houses, through parks and under bridges.

The latest monitoring carried out by the former Auckland Regional Council found Puhinui was the dirtiest stream out of the 31 it tested.

Jenks says the tests are misleading because they were taken at the stream's dirtiest point.

But Puhinui's visible and measurable changes from top to bottom show the stress which development places on waterways.

Though junk and pollution events influence the stream's poor state, the most harmful pollutants are more insidious. Solvents, stormwater, and the slow trickle of manganese, cadmium and toxins make their way in from roads and nearby factories.

A Weekend Herald walk along the Puhinui's length found it was a tale of two streams.

Trickling out of Totara Park in Manurewa, you could mistake the top of Puhinui stream for a pristine part of the Waitakeres. Crystal-clear water cuts beneath a canopy of ferns and rata, the quiet only disturbed by tuis singing and truant schoolkids swimming in one of its shallow pools.

As soon as the Puhinui slips under the Southern Motorway, the dirty stamp of development begins to show. The water is still clean, but traffic cones, tyres and corrugated iron punctuate the stream bed.

The waterway is then piped under the new southwestern motorway twice, and despite pockets of replanted banks, its canopy is mostly stripped away, until it emerges, murky, from between a row of factories.

This is where the stream was monitored by the ARC. The 2010 River Quality report says it regularly exceeds acceptable levels of pollutants - nitrogen, phosphorus, zinc - and one in five of its tests failed to return an acceptable level of health.

This meant a fifth of the time it could not sustain its own ecosystem: fish, invertebrates, birds, and plant life would struggle to survive in it.

An "acceptable" temperature to sustain life in the stream is 21C. On several tests, the stream had warmed to 24.7C.

The Puhinui's water, tainted by the waste of the suburbs, sluices into the Manukau Harbour.

Environmental scientist Neil Mitchell, from the University of Auckland, says most Aucklanders do not make the connection between the city's urban streams and its prized harbours.

"If we were to get the streams cleaned up, the harbour would be clean. I wouldn't dream of eating shellfish from the harbours, because I know about all the stuff that goes off the land into the streams."

He reminisces about the time, 30 years ago, when children used to net whitebait at the mouths of the city's urban streams.

"As some Maori say: 'The ocean starts at the mountaintop'. The water carries all our pollutants, whether it's from the road or your back garden. Water is what links all aspects of the environment."

To illustrate the connectivity of ecosystems, Jenks cites a stream restoration project in the Whaingaroa Harbour in Raglan. In 1994, before the restoration, it took an average of 12 hours to catch a fish in the harbour. After eight years of work on the waterways which flowed into the harbour, that was drastically reduced - to 12 minutes.

There are many priorities for the restoration of the Puhinui - preventing downstream pollution, conserving native species, protecting public health, and improving aesthetic value. But is it salvageable?

Auckland Council research, investigations and monitoring manager Grant Barnes says to raise Puhinui to an "excellent" water standard (like the Cascades in Waitakere) would require bulldozing of the suburbs which crowd its sides.

Barnes says Puhinui suffers from urban stream syndrome. Urbanised areas create lots of hard, impervious surfaces - roofs, playgrounds, carparks - which do not let water feed through the soil and into the waterways. This means the stream is often too warm to support aquatic life, more prone to flooding, and does not have a steady flow to flush out contaminants.

The council is looking to introduce low impact urban design, such as swales - indents to manage runoff and trap contaminants - but the uptake is slow, and retrofitting is costly to the ratepayer.

Barnes says complete conservation is probably unattainable, but mitigation is possible.

Everyone who works on the stream agrees on one crucial factor - community buy-in.

Dr Mitchell says: "The council cannot find the money to fix all these things. People are just not aware of the streams in their backyards. If 1.4 million people took just a little more care, that's a huge effect."

Unitec senior lecturer in landscape architecture Matthew Bradbury says Auckland should aspire to beautifying urban streams as much as its waterfront.

"The waterfront is great if you're rich. But Aucklanders can re-orientate themselves."

He says the first step is building walkways and cycle paths alongside streams, which draws residents' attention to spaces otherwise fenced off, or sliding behind factories.

"This isn't Utopian - it's already in place, in the North Shore, in Waitakere," said Bradbury.

But community involvement can be light on the ground near the Puhinui. Jenks says South Auckland is a hard-working environment where both parents have jobs and don't have much time for conservation.

Therefore Wai Care focuses on recruiting children, hoping they will grow up with green ideals. This has led to some heartening moments - 65 kids from Wiri Central School recently gave up their lunch hour to plant trees by the stream.

"Sixty-five kids! From a hard school. And they worked like hell," says Jenks. "It was beyond heartening. You can never second-guess what kind of interest might be out there. You've got to just dig in and keep doing it."

Amid the council's struggle to improve the stream's water quality, it has had some successes - a network of fish ladders allows native fish to use it as a corridor to their ideal habitat.

In Barnes' words, "There is a surprising amount of life in there. These streams are more than just conduits for waste, if Aucklanders cared to look ..."