How swimmable are the rivers in the Nelson Tasman region?

Children playing in Nelson's Maitai River.
BRADEN FASTIER

Children playing in Nelson's Maitai River.

When the Government released its new standards on water "swimmability" last month there was much confusion about what they represented. Charles Anderson reports.

It should be a simple question to answer. Can you swim in our region's rivers? Will I get sick if I go up the Maitai or the Lee Valley? For the record, the answer to both those questions is a highly probable "no".

But when Environment Minister Nick Smith presented to a crowd at the Cawthron Institute last month there was a caveat from Nelson mayor Rachel Reese.

The Wakapuaka River at Paramata ...
Colin Smith

The Wakapuaka River at Paramata Flats. / The Nelson Mail.

"These are incredibly complex issues," she said. "I think it is really important that we understand the science around this."

The Government's goal was to make New Zealand rivers 90 per cent swimmable by 2040. It was a bold move that Smith hoped would show how dedicated his party was to the health of our waterways. The good news, he said, was 72 per cent of them were already were "swimmable".

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A map showing the swimmability of rivers in the Nelson Tasman region.
Ministry for the Environment

A map showing the swimmability of rivers in the Nelson Tasman region.

The Ministry for the Environment had come up with colour map to help decode the complexity. Red was bad. Green was good. Orange was acceptable. Taking all those measures - of Nelson and Tasman's 1757 km of rivers and lakes, Smith told the Cawthron audience, 96 per cent was swimmable. However in Nelson alone, 100 per cent of the rivers were swimmable.

This came as a pleasant surprise to Nelson city councillor Mel Courtney last week when he asked about the council's response to the standards.

Group manager strategy and environment Clare Barton told Courtney that the city's rivers were already above the required threshold.

Hira School pupils study insect life in the Wakapuaka River.
Martin de Ruyter

Hira School pupils study insect life in the Wakapuaka River.

"So we are there now? In your view?" Courtney asked.

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"The rivers that have been identified in the swimmability maps are the larger ones in the region," Barton replied. "There are smaller tributaries that do have water quality issues that are not reported. So there is still further work to do."

Which was part of the contention. The Government's goal of "90 per cent" of rivers really only meant of 90 per cent of rivers that it deemed able to be swum in. This represented only about 10 per cent of all waterways.

Nelson Labour candidate Rachel Boyack also suggested that there were rivers that had failed Nelson City Council's own reporting standards for safety but came up "fair" under the Government's new standards.

The Wakapuaka River at Paremata Flats near Cable Bay was last year classified as "very poor" due to five incidences of elevated bacteria counts measured during the 2015/2016 summer monitoring of the river.

Monitoring of the river there started in 2008 but has had a "very poor" or "poor grade" since then.

"The elevated bacteria are from livestock, with unrestricted access to waterways and also from numerous wildfowl that congregate on the flats," the council says. It says that people should not swim there.

So why the discrepancy?

How can a river at once have "fair swimmability"  and then then also have "very poor" swimmability?

The issue is that the Government's swimmable standard now has a number to define it - 540 E coli per 100 millilitres of water.  If a river meets that standard 80 or more per cent of the time, it gets a fair, good or excellent marking. If it doesn't, it gets an "intermittent" or "poor" rating.

The Ministry of Health says that if you swim in a river that has 540 E coli per 100 millilitres of water then you have a one in 20 chance of getting sick. Critics have said this an unacceptable level of risk.

To be considered "fair" under the new rules the estimated risk of Campylobacter infection (resulting from E Coli) should be less than 1 in 1000. And 10-20 per cent of the time, the estimated risk of Campylobacter infection is less than 50 in 1000.

However, Smith says most most rivers, especially in the Nelson region, do not cross that threshold very often and when they do it is usually after a high rain event.

He told the Cawthron audience that it was very unlikely that a family would want to go swimming in a river that was in flood, not just because the bacteria risk was higher but because the it was simply dangerous to swim in.

"Even our cleanest rivers breach swimming water quality standards during storms," he said.

So swimmability really means the probability of getting sick.

Hence Paremata Flats. The likelihood of getting sick there was one in 20 for only five days over the 2015/16 period. This was the council's time span of measurement. On the ministry website however, it uses a different time frame - from this past December - which means it only breached the E Coli level three times, which represents an acceptable level of risk according to the new standards. 

The goal is estimated to cost the Government, farmers and councils $2 billion over the next 23 years.

Smith has used the word "practical" to describe the goal. It isn't practical, he said last year to include every river in the entire country. If it were it would include 10 times more rivers and lakes and the cost of cleaning up all of them would likely exceed 10 times $2 billion.

But also the measure it has used, E Coli, represents only one way to measure a waterway's health.

Some rivers that have technically fallen under the "swimmable" rating are actually "unswimmable" for different reasons. Some have toxic algal blooms fuelled by dry conditions and nitrogen levels and others because they don't have any water in them. However, there isn't any E Coli in them so it passes the Government's test.

All of this has led to a confused and haphazard explanations of the new plan. Some critics, like Forest and Bird's Kevin Hague, have said the goal not only misrepresents the state of our waterways but will lead to an overall decline in their health. 

But Rachel Boyack believes she has a simple test of Smith's goal.

"If Nick Smith truly stands by his analysis of the health of New Zealand's rivers and believes that the Wakapuaka River is 'swimmable' at Paremata Flats, then he should back up his analysis by taking a dip in the river."

By the ministry's analysis though, the probability of him getting sick is still reasonably low. But there is only one way to be sure.

 

 - Stuff

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