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ESR leads the charge in checking our waters are safe for swimming

30 May 2023

Swimming water
Water Quality Surveillance Er
Water Quality Surveillance Er

Dr Margaret Leonard, a senior water microbiology scientist at ESR, is leading a three-year $5.8 million Jobs for Nature project gathering freshwater field data to model potential health risks from swimming. Along with a number of other projects, the goal is to improve New Zealand’s freshwater quality and increase engagement with iwi and hapu. Nine councils are involved in collecting 732 samples from 40 water bodies to help create a new model that will support NZ’s freshwater recreational guidelines.

New Zealand’s current freshwater guidelines are based on a quantitative microbial risk assessment (QMRA) of freshwater carried out over 20 years ago. Last year, Land, Air and Water Aotearoa (LAWA) data found two-thirds of monitored swimming sites presented a potential risk to public health. The government’s Policy Statement for Freshwater Management has set a national target to improve water quality by 2040, so that more rivers and lakes are suitable for freshwater recreation.

Guidelines that reflect the risk

This new quantitative microbial risk assessment responds to the changes in land use, improved waste management practices, and applies new analytical techniques. “The goal is to build a database, that accurately reflects the New Zealand situation right now and to develop tools that can better assess the current health risks from pathogens,” says project lead Dr Margaret Leonard.

Most of the sites being sampled are current or former swimming spots, with some evidence of faecal contamination. “We are deliberately looking at sites with poor water quality, so they’re not representative of water quality in general,” explains Dr Margaret.  

ESR is using a new technique called microbial faecal source tracking that wasn't readily available 20 years ago. It can identify if faecal contamination is from wildfowl, ruminant or human faecal sources. This level of detail can directly link faecal contamination with the source present during the sampling event, rather than relying on the assumption that the faecal contamination comes from the dominant land use, for example, urban, farming or birds. “We’ve found unexpected faecal sources sometimes turning up. More accurate information on the source of contamination informs the councils about what they need to do to improve the poor water quality,” says Dr Margaret.

ESR's Dr Sarah Coxon showing a local council how to filter large-volume samples in the field so that filters can then be analysed for protozoa in the lab.

Sampling and upskilling at the same time

The project funds nine councils around New Zealand to collect the freshwater samples. It also helps these councils build their environmental monitoring capability and capacity, allowing them to carry out other freshwater management work, such as assessing barriers to fish passage or new water quality monitoring.

Sampling will finish in June 2024 to cover seasonal effects. The field data will then be used in the QMRA model to assess the risk to human health from pathogens.

“ESR and MicroAquaTech at Massey University are measuring common waterborne pathogens that cause stomach upsets. ESR is also measuring bacteria that indicate faecal contamination has occurred, as indicator bacteria are much easier and more cost effective to monitor than pathogens,” explains Dr Margaret.

“ESR has also got the expertise in risk assessment. Our science makes that important connection between health risk and the environment – in particular the link between water quality and people’s health,” she adds.

A uniquely New Zealand approach

Overseas, an epidemiological approach has been taken to setting recreational water quality criteria, using bacteria that indicate there has been faecal contamination. For example, people are asked to report on their health after swimming at a beach.

New Zealand’s population is too small to undertake such an epidemiological study. Also, most overseas studies have occurred where the source of the contamination is from human sewage, whereas New Zealand freshwater bodies may receive a lot of ruminant and bird contamination. “That’s because freshwater spots in New Zealand tend to be more rural, and while some sites are affected by human sewage, the Havelock North Campylobacter outbreak showed that pathogens from ruminants can make people very sick as well,” explains Dr Margaret.

“That’s why it’s important to take a New Zealand specific approach in assessing the risk, because we’ve got quite mixed sources of potential contamination in our recreational areas,” she adds.

The new, up-to-date quantitative microbial risk assessment will use current data to assess the risk of recreational water use and give us a better understanding of the association between pathogens and indicators.