The Nats’ new ‘swimmable’ rivers aren’t

Anthony R0bins
7 years ago
Categories: Conservation, farming, farming, sustainability, water
Tags: david parker, dodgy statistics, nick smith, water, water quality

I’ve been waiting for the dust to settle a bit before wading in to the Nats’ water quality fiasco.

Nick Smith bungled the announcement hugely, allowing the perception that they were going to reach their new goals by allowing twice as much shit in “swimmable” rivers. He then released some incomprehensible statements and called critics “junk science”. Unfortunately the critics are more or less right. An excellent piece on RNZ:

Diving into the muddy water of ‘swimmable’

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Previous water quality guidelines had separate criteria for swimming and other activities. A river or lake was graded an A for swimming if tests for the E coli bacterium came back with less than 260 bacteria per 100 ml of water 95 percent of the time.

The criteria for an A for other activities was less strict; the median (middle) value of all the tests taken over a year needed to be less than 260 bacteria per 100 ml. A river or lake got a B if the values were 260-540 E coli, a C if they were 540-1000 and a D if they were over 1000. So, under the old guidelines, some of our lakes or rivers could easily have an A for water sports but a B (or no rating at all) for swimming.

In the government’s new policy document (‘Clean Water’ – PDF, 3.68MB), the threshold number of E coli has been set at 540 bacteria per 100 ml of water. Now to get a blue (“excellent”) rating, the water must have less than 540 E coli for 95 percent of the time.

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This is where the government’s new definition of swimmable comes in: blue, green or yellow graded water. In other words, it can be above the threshold for up to 20 percent of the time.

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The ‘Clean Water’ document itself is a bit misleading because the new regulations require that at least half the time the E coli levels must be lower than 130 per 100ml, so that the risk of getting Campylobacter is very low – but it can be higher than one in 20 for 20 percent of the time.

What this means is that your chance of getting sick isn’t one in 20 every day. It varies. Sometimes it’s much lower than that and sometimes it’s much higher.

We’ve crunched the numbers so you can see how that risk changes for each of the “swimmable” categories of water. The risk ranges from less than one in 1000 (0.1 percent), to one in 100 (1 percent), one in 20 (5 percent), one in six (15 percent) and even higher.

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The tricky bit is not knowing which days are which, as water can look perfectly swimmable but still have dangerous levels of Campylobacter in it.

What kind of ‘swimmable’ river is that?

Regional councils are meant to notify the public if the E coli levels go above 260 bacteria per 100 ml, so it looks like it’s worth checking before immersing yourself in any “swimmable” New Zealand rivers and lakes.

What kind of public safety is that?

Under the new standards we have up to a 1 in 6 risk of serious infection at the times that we actually swim in rivers, and Smith is trying to hide this fact by fudging around with year-long averages. So (unsurprisingly) David Parker was bang on yesterday:

Labour’s David Parker calls for ‘swimmable’ test to reflect when and where you take a dip

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Yes, he [Smith] has moved the goalposts. He is now classifying as swimmable rivers that would not meet the current understanding of swimmable in New Zealand. It’s not fair for him to say that on the basis it’s a higher standard than wadeability that it’s an adequate standard for swimmability because it’s not. I think there should be a 99 per cent confidence level that you won’t get crook.

A river can exceed the E.coli limit up to 20 per cent of the time and still be graded as swimmable. That is 2.4 months a year. This really irks me. From Christmas until the end of February is less than 20 per cent of the year. River quality generally gets worse in summer when flows are lower and water temperatures are higher. It’s also when most people swim in our rivers. Any standard which ignores that reality is rubbish.

Well worth reading the whole interview.

Smith can rant all he likes, but the fact is that this is where we are:

Unswimmable lagoon now deemed swimmable under revised standards

A waterway that Environment Minister Dr Nick Smith once deemed “impossible” to improve to a swimmable condition would be considered swimmable under proposed new standards.

Several other waterways – including dry shingle beds and rivers with toxic algal blooms – would also meet the swimmable standard, despite clearly being unsuitable for swimming.

Critics have said such instances reveal shortcomings in the way the proposed standards are measured.

Also worth reading, Newshub’s series on water. A lot of the pollution is from general agriculture and urban runoff. This is a complex and serious problem requiring complex and serious solutions. Not Nick Smith.