Diving In: How to Determine if Your Go-To Swimming Spot is Safe for Splashing!

Trends for our lakes are not much more promising, with two-thirds categorized as in poor or very poor condition; however, nearly 70% of upland lakes still remain in fair to very good state.

Areas with the worst rankings for E. coli levels are often surrounded by pastoral landscapes such as dairy fields or urban environments, while those adjacent to indigenous and non-native forests exhibit significantly cleaner conditions.

Information gathered by the collaborative Land, Air, Water, Atmosphere (LAWA) initiative reveals that numerous river locations consistently rank poorly for the harmful bacteria over the long term.

Many of these locations – including Kaiate Falls in the Bay of Plenty, the Rere rockslide into the Wharekōpae River near Gisborne, and Selwyn River at Coes Ford in Canterbury – are also favored areas for recreation.

Conversely, monitored coastal locations throughout New Zealand are generally considered safe for swimming most of the time – with the exception being coastal lagoons.

“Although lagoons might appear to be a safer choice, particularly for young children, since they are warmer and lack swift currents or waves, they typically exhibit lower water quality,” explains LAWA’s science lead, Dr. Elaine Moriarty.

“This is often due to an abundance of birds and their droppings, all floating around in a cozy, gently flowing body of water – ideal for bacterial proliferation.”

Do consistently low long-term ratings imply these spots are perpetually unswimmable?

Not necessarily: the long-term rating is based on risk and does not always indicate the conditions on any specific day.

LAWA’s “Can I swim here?” interactive website maintains regularly refreshed water quality data for over 850 locations.

“We have learned from monitoring data that the majority of swimming areas in New Zealand are suitable for swimming the majority of the time, but there is always a potential for risk.”

Those locations that have received poor ratings over the last five summers reflect a varied range of water quality results.

“Poorly rated locations might include those that have often been safe for swimming but have occasionally surpassed the threshold for swimming safety once or twice each season, as well as those that frequently exceed swimming water quality standards,” she remarks.

Numerous favored swimming areas are also known to surpass the guidelines following periods of heavy rain, which can introduce contaminants such as wastewater or agricultural runoff into rivers – yet otherwise might have acceptable water quality.

“That’s why we encourage swimmers to refrain from entering the water for two to three days after significant rainfall, regardless of the most recent monitoring findings or the long-term evaluation.”

Is there a chance I will fall ill if I swim in contaminated water?

It’s not assured, but immersing oneself in water with high levels of

Faecal microorganisms such as E. coli imply that you face the danger of various undesirable symptoms.

This can include nausea and loose stools, respiratory infections, or infections of the eyes, ears, nose, and throat.

LAWA’s platform employs a traffic light system to indicate the health risks at each swimming location, with green denoting safe conditions, amber warning caution for vulnerable groups like the very young and elderly, and red indicating to avoid.

Moriarty suggests that individuals can conduct a straightforward test to prevent illness at their local swimming area by standing in water up to their calves and observing what lies beneath.

“If you can’t see your toes, it’s best to stay out.”

What are additional dangers to keep an eye out for?

Generally, individuals should refrain from entering the water if it appears cloudy, has an unpleasant odor, is rapidly flowing, or if there are signs advising against swimming.

A significant threat is harmful algae, which flourishes in waterways under conditions of low rainfall, elevated temperatures, suitable nutrient levels, and ample sunlight.

“These conditions often align during a Kiwi summer,” Moriarty notes.

“The dark brown-black mats of toxic algae are frequently observed in certain rivers, and several lakes are susceptible to pea-green or reddish-brown toxic algal blooms.”

Though naturally occurring, even a minute quantity of toxic algae—imagine the size of a 50-cent coin—can lead to severe damage if ingested.

“For humans, contact with toxic algae may result in nausea, diarrhea, and skin irritation, and there is a risk of serious poisoning in small children if ingested,” she warns.

“Sadly, many dogs in New Zealand have succumbed to toxic algae. If your dog consumes harmful algae, you should take it to a veterinarian immediately.”

Jamie Morton specializes in science and environmental journalism. He began working with the Herald in 2011 and covers topics ranging from conservation and climate change to natural disasters and emerging technologies.