Water qualilty and Health Warnings

I recently published a couple of health warnings about popular swimming holes in Katikati - the Henry Road ford on the Uretara River and McMillan Road on the Tuapiro Stream.

It subsequently came out that a local lad has been seriously ill in hospital with ecoli poisoning after swimming in the Uretara.

Logically, people have asked where is the contamination coming from and what can we do about it. Western Bay of Plenty District Council published these notices but the information and expertise comes from  Toi Moana Bay of Plenty Regional Council, so here is some very valuable information from a real expert, James Dare, a water quality environmental scientist at the regional council.

I asked James if what I had heard about geese being the source was correct and whether it was a case of us sampling more (so finding more) than we used to. 

He put me right on both counts, so here is James' expert thoughts on the contamination:

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I’m really sorry to hear about the local boy who is in hospital after swimming in the Uretara.  This site has been one of our problem sites for a number of years, which is the reason Toi Te Ora have a permanent health warning advising against recreational water contact in this area.  Last season (October 2023-April 2024), 27% of the samples we collected from the Uretara at Henry Rd Ford site were above the safe swimming standard (550cfu/100ml).  This ranked the site as the second worst monitored bathing site in the BOP, after Kaiate Falls (see bar chart, attached). 

You are partly correct about geese defecating in the water, however we think the problem is more complicated than that.  The upper part of the Uretara Catchment is very steep, so faecal matter is mobilised very easily with any significant rainfall.  This shows up in our forensic source testing samples as a ‘ruminant’ signature, which means that it’s likely coming from cows, sheep, or deer.  The ruminant signature is more common in the water in the upper catchment, but is also found in the lower catchment, near the swimming hole, after heavy rainfall. 

The avian signature you talk about, shows up in the lower catchment during drier periods.  Most waterfowl tend to like the lower part the catchment because the habitat is more suitable for them, i.e. the river slows down, it gets deeper, and there are more food sources.  We did find a number of wild geese nesting along the riverbank, upstream of the swimming hole, however E. coli results remained elevated after these geese were removed, which suggests that this was only part of the problem. We also found a lot of Pukeko DNA in the river, which are commonly found in wetland scrub areas in the lower catchment.

So long story short, it’s complicated.  The steepness of the catchment and land use contribute ruminant faecal bacteria to the stream, which is more harmful to humans than avian faecal bacteria.  But waterfowl and pukekos are common where people swim in the lower catchment, and this form of contamination is present during drier periods when people are more likely to be swimming. 

Yes, the avian source is technically natural so you could assume that the avian problem has been around for a long time before we started monitoring the stream comprehensively in 2015/2016.  However, you can see in the figure below that results are becoming more consistently high, which suggests that it’s not just natural contamination (see attached sample chart marked "Uretara at Henry Road ford".)

The Tuapiro is a bit different because elevated E. coli results tend to be caused by rainfall events, and results return to normal after a few days.  I have talked to Toi Te Ora and can confirm that there is no health warning on the Tuapiro Stream.  The Antenno notification seems to have been generated based on the most recent sample results which were collected on Tuesday.  This is technically not the same as a health warning but indicates that conditions at the time of sampling were unsuitable for swimming.  I would expect conditions to return to ‘normal’ fairly quickly after bad weather (see attached sample chart marked "Tuapiro at McMillan Road"

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Thanks James Dare for sharing this. There is a lot of mahi to be done to protect our whenua (thankfully,Project Parore and others are already active in this work)