The dubious water quality of the Paris river where Olympic triathlon events were held is no secret. But New Zealand swim spots are notoriously prone to faecal contamination too. So which is worse?

Hayden Wilde, a New Zealand triathlete who won silver in the men’s individual event at the Olympics in Paris last week, fell sick with E. coli after his race. Symptoms, which include diarrhoea and stomach cramps, are unpleasant, particularly if you’re about to compete in a mixed relay at the world’s biggest sports contest, as Wilde was on Monday. His source of exposure isn’t hard to guess: swimming 1.5 kilometres as fast as you can in the khaki-coloured Seine, surrounded by the thrashing limbs of other athletes, is basically a guarantee that you’ll get water in your mouth.

The day after the race last week, Wilde felt rough. “I ran for an hour and there were a couple of loo stops within that hour,” he told One News. “Then went to the pool, I was pretty depleted, I was real tired. I was lucky I was able to eat really well. That night I was feeling 80% better.” He improved enough to appear in the mixed relay on Monday, although he ended up crashing his bike, and the New Zealand team came 14th. 

Concerns around the water quality in the Seine were well publicised in the lead-up to the Games, and athletes have been well aware of the risk. Last week US triathlete Seth Rider said he was building up his E. coli tolerance by not watching his hands after using the bathroom. Spoiler alert: experts were quick to point out that this does not work. Instead, one of the best ways to avoid getting E. coli is to simply not swallow lots of water filled with E. coli. Wilde, meanwhile, told Newshub before the Olympics he was more worried about a Netflix movie that portrayed a shark in the Seine than E. coli, but turns out confidence doesn’t make you immune to wily bacteria. 

After practices being cancelled and both the men’s and women’s triathlons being delayed due to high levels of E. coli, on July 31, the day both events were finally held, the concentration level was just under 1,000 E. coli per 100ml, falling within World Triathlon’s guidelines, although only just. However, a more comprehensive count recommended by water quality experts Fluidion, which takes into account clumps of faecal matter as well as small free floating particles, registered over the limit. The enterococcus level, the other bacteria monitored by standard water quality monitoring for human health, had just dipped beneath 250. 

The water contamination levels World Triathlon’s guidelines allow are many more times higher than what is considered acceptable by water monitoring standards in New Zealand. Environmental Health Intelligence New Zealand says that a safe E. coli level is less than 260 per 100ml, and less than 140 enterococci per 100ml. At levels slightly higher than this, water is still most likely safe but should be avoided by vulnerable people, while beyond 550 E. coli and 280 enterococci per 100ml puts the water into the “unsafe” category. Other organisations, including the US Environmental Protection Agency, set a limit of 126 E. coli units per 100ml of water and say that higher levels aren’t suitable for recreational use.

According to World Triathlon’s rules, decisions about whether an event should go ahead should be made based on WHO guidance, weather forecasts and sanitary inspection. (This includes noticing how the water smells, and whether there are any patches of garbage which might have attracted rats.)

While unable to comment specifically on World Triathlon’s rules, Martin Neale, technical lead for Safeswim, an initiative that aims to reduce public health risks at swimming sites in Auckland and Northland, told The Spinoff “the indicators and thresholds that we use in Aotearoa are based on scientific research that was undertaken here.” The levels are based on epidemiological studies conducted in New Zealand in the 1990s and early 2000s.

In the last decade, as awareness of water quality issues in New Zealand has spread, it’s become second nature for many people to check water quality – whether on Can I swim here? or Safeswim for Auckland and Northland.

In cities, the main problem with water quality is overflow from ageing sewage pipes, which discharge extra water when it rains. In Auckland, a $1bn massive sewage tunnel called the Central Interceptor will be completed in 2026, and one outcome of the project will be less contamination on the city’s beaches. Outside of New Zealand’s cities, the main cause of poor water quality is agricultural run-off, from animal waste and fertilisers. 

So how does the Seine compare to a New Zealand beach after heavy rain? While the acceptable limits are different, instances of heavy pollution are the same. In June, following rain, the amount of enterococci in Owhiro Bay in Wellington reached 1,800 per 100ml. Te Auaunga/Oakley Creek, which travels through central Auckland and has a long-term “do not swim” alert on Safeswim, has had a median of 800 E. coli per 100ml for the last five years.

Land Air Water Aotearoa, a website that displays water quality monitoring from councils across New Zealand, will mark a location as red if it has 540 E. coli or 280 enterococci per 100ml, a standard that 12 sites in Auckland are currently surpassing, including Cox’s Bay near Ponsonby and the lagoons in Piha. Cox’s Bay and Piha South Lagoon have long-term do not swim notices in place.

On Safeswim, an Auckland swimming spot gets a red flag if enterococci levels suggest there’s more than a 2% chance of getting sick from swimming there, while a more serious black flag is triggered by direct faecal contamination from wastewater overflow, usually after heavy rain. St Mary’s Bay in Auckland, for example, once surpassed 5500 enterococci per 100ml. It’s harder to get up-to-date statistics from other parts of the country, however, as most councils don’t monitor water quality in winter. But out of 50 water monitoring sites in Canterbury, last year all but three failed to meet E. coli standards. 

Contaminated water is bad for people, especially because it limits the use of rivers and the sea for important social and cultural activities like swimming and gathering kai. It’s also terrible for the animals like insects and fish, which don’t have the choice to leave the water when it’s polluted.  

This problem isn’t unique to New Zealand, of course; at the Olympics, the water quality of the Seine has been a big issue. Anne Hidalgo, the mayor of Paris, went for a swim in the Seine in the middle of July to show that a decade of efforts to clean up the iconic waterway in the French capital had worked. Those efforts, totalling more than 1.4 billion Euros, included building an enormous underground “cathedral” to contain stormwater, increasing the city’s capacity to absorb rainfall, just as the Central Interceptor hopes to do for Auckland. The water quality in the Seine will likely continue to improve, meaning that in the future, without the frenzy of the Olympics, people in Paris will hopefully be able to swim in the central city river. 

The Olympics organisers blamed climate change for the unpredictable rainy weather causing the high pollution levels. Despite the delays, the men’s and women’s triathlon went ahead, as did the mixed relay on Monday – even if Belgium pulled out because one of their athletes was too sick to compete. Meanwhile, Seth Rider, the American who had stopped washing his hands, was able to compete for the US. Their team came second.