“If the temperatures do increase, people are more likely to be around their rivers or streams or beaches in the local area,” Hurst said.
“So it’s probably more important than ever that they check the Lawa website just to make sure that they’re swimming in spots that have good water quality.”
Water quality testing results are posted on the Land Air and Water Aotearoa (Lawa) website, with up-to-date public advisories.
The samples from the sites are tested for levels of faecal contaminants - E. coli in freshwater and interococci in saltwater - and toxic algae levels.
These results are checked against guidelines published by the Ministry for the Environment and the Ministry of Health.
Whichever level comes back highest, faecal or algae, is the status the site will assume.
“Those two components form that swimability grade,” Hurst said.
“The worst of those two grades informs the alert that we put out.”
Hurst said there were general guidelines for staying safe in clean water.
Swimmers should avoid swimming during, and for 48 hours after, heavy rain. The water should be clear, clean and odour-free.
Some spots flagged with poor water quality may not be obvious to swimmers and remain in poor quality without recent rainfall.
The two streams at Kai Iwi Beach are flagged red due to their consistently poor quality.
“They can have high E. coli results even when the water is clear and it hasn’t rained,” Hurst said.
“Even if you follow those two guidelines, you can still be faced with high indicator bacteria in the streams.”
The streams are known for consistently high levels of bacteria over the past five years of testing, regardless of how Kai Iwi Beach tests, and have a permanent red warning on Lawa. Horizons and Health NZ Te Whatu Ora have put up permanent signs advising against swimming in the streams.
The streams often tested poorly because of a combination of urban and agricultural runoff, Hurst said.
“Unfortunately, for families and especially small kids, those small, little streams are seen as really safe to swim in.
“But from a water quality point of view, often the beach is better.”
Ototoka Stream was permanently marked as unsuitable for swimming with poor water quality caused by similar reasons to the Kai Iwi streams, Hurst said.
From 137 samples taken within the past five years, the site tested at red warning levels of E. coli for 55% of the tests, amber 31% and green 14%.
The Turakina River Mouth does not have a permanent warning but tested positive for E. coli levels when it was last sampled on January 6, with an amber caution issued.
Other sites, including Lake Wiritoa and Dudding Lake, have been flagged with amber warnings due to their algae levels.
Hurst said Dudding Lake was 100% swimmable and Lake Wiritoa 90% swimmable from a faecal levels standpoint in the most recent testing.
“That’s what we would expect for these lakes,” he said.
“It’s very uncommon for them to have problems with faecal contamination.”
“But generally what does drive the swimability in the lakes, and it’s the same almost every year, is that potentially toxic algae.”
Cyanobacteria is a common, naturally occurring algae which can be toxic to humans and pets.
It can appear as green or black scum at the edge of waterbodies and on rocks.
“Things like increased runoff or nutrients into a lake can drive cyanobacteria as well as increased temperatures.”
As summer temperatures rise, Hurst said it was a good idea to always check the Lawa website on where was best to swim or call Horizons or Health NZ with any questions.
“Lawa is a good place to check in ... but it’s also a great place to find new swimming spots as well across the region.”
Erin Smith is a multimedia journalist based in Whanganui.
