These are Christchurch's most polluted streams
An unassuming section of Christchurch's Heathcote River has won a dubious honour – it has the city's unhealthiest water.
A recent surface water quality survey by the Christchurch City Council revealed the river met few water quality guidelines.
Overall, 98 per cent of the city's monitored waterways failed at least one guideline for water health, a result consistent with previous years.
It was the Heathcote, however, that continued to be of most concern, having recorded higher levels of zinc, nitrogen, and suspended solids.
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Tracing the causes of the Heathcote's pollution takes you to the city's south-west, where the river begins.
Two tiny waterways, the Haytons and Curletts Rd streams, are having a big effect on the Heathcote's health.
They both flow from heavily industrialised Wigram, where they are pumped directly with stormwater filled with heavy metals such as copper and zinc, which flow down the streams and into the Heathcote.
After heavy rainfall, zinc quantities can be five to 10 times higher than the maximum allowable value.
Testing showed the streams failed virtually every water health guideline and were so packed with metals that life would not survive in either.
It won them the dubious honour of Christchurch's unhealthiest waterways.
A 2014 investigation into poor water quality at Haytons stream determined that it was not getting better, and businesses in the area were not improving their management practices.
Drains connected to industrial activity can be seen dotted along the stream.
They are both a prime example of "urban stream syndrome", a problem that has crept up on Christchurch over many decades of urbanisation.
Haytons and Curletts roads were being targeted by authorities due to their effect on the Heathcote.
Christchurch-West Melton zone committee chairman Arapata Reuben said the problems with the streams were well known, and they were being dealt with as a high priority.
While newer developments such as Wigram Skies had ways to stop contaminants from reaching the waterways, older areas, like those near the streams, did not.
"The challenge is how to put those types of infrastructure into an already urbanised area," he said.
It could take 80 years to reduce the amount of zinc in the city's rivers, the city council said recently.
A proposed treatment system in Woolston would reduce the Heathcote's dissolved metal levels by 20 per cent, and sediment by half.
Metals choke the life out of a waterway when found in large quantities. They were a distinctly urban problem, said Dr Bryan Jenkins, a professor of strategic water management.
"You would expect the heavy metals to remain in the system. There would be some removal, but they're basically pollutants that when they start in a tributary, they end up in the river system," he said.
"We are getting copper and zinc into our rivers coming from roofs. It's rare to find heavy metals in rural areas – they're certainly urban-type pollutants."
The Haytons and Curletts roads streams had consistently had problems, he said.
The solution had to begin at the source – effectively, stop putting the contaminants in the water in the first place.
"The key thing is reduction at the source. You can put in in-stream treatments, but the best thing is removal at source."
Nearby is the Cashmere Stream, the largest tributary to the Heathcote.
It too has problems, often completely brown with sediment which ends up in the Heathcote.
The second worst waterway in the survey was at a point near Halswell, which had a 29 per cent increase in zinc concentrations.
Resident Gordon Rudd has lived near the Cashmere stream for several decades. In 2010, he began measuring the stream's water clarity every day.
"The clarity of water has probably decreased," he said.
More water was coming from newer subdivisions such as Aidanfield and Westmorland, which was affecting water clarity, he said.
He was hopeful about the stream's future. There had been a concerted effort to improve the water.
"Over the last 10 or 12 years there's been a great deal of effort in looking after the health of the Cashmere Stream," Rudd said.