Coes Ford water sampling enables nationwide study

Selwyn's Coes Ford may be a top spot for swimming, but it may also hold the key to unlocking the relationship between E. coli and harmful waterborne pathogens, thanks to a nationwide pilot study conducted by the Crown-owned Institute of Environmental Science and Research (ESR).

Before the March-April lockdown due to COVID-19, Environment Canterbury surface water scientists Jarred Arthur and Emily Gray were tasked with carrying out the sampling and testing of water in the Selwyn River at Coes Ford, and the Heathcote River in Woolston, Christchurch – as part of the study for Ministry for the Environment (MfE) and the Institute of Environmental Science and Research (ESR).

More broadly, the study is investigating the relationship between faecal indicator bacteria and harmful pathogens (bacteria, viruses and protozoa) in water.

The Coes Ford and Heathcote River sites were chosen as part of a network of rivers across New Zealand and are a good representation of some of the issues facing swimming water quality in both the rural and urban sectors.

What does Environment Canterbury hope to gain from this study?

Jarred said by establishing a relationship between E. coli, other pathogens, and their source in the water, scientists hope to be able to predict the human health risks of where and when harmful pathogens will appear.

“There are a lot of land-use pressures including agriculture, urban pressures (e.g. stormwater), and waterfowl or other nesting birds,” he said.

“All those pressures add up on the water, and so we’re helping measure how those pressures are different in waterways around the country.

“This is very important, as it is all about protecting public health. Our waterways are important ecologically, culturally and aesthetically, but also for swimming water health and that’s what this project is directly related to,” he said.

Emily said while microbes are what the pilot test is focused on, there are some potentially hidden dangers at sites such as Coes Ford.

“Coes Ford is a contact recreation site, so we monitor a few things that could be a human health risk,” she said.

“E. coli is often focused on, but another large part of the health risk is toxic cyanobacteria. At Coes Ford, this forms as a thick black mat that can be found on the bottom of the river.

“The mat produces a cyanotoxin which is potentially deadly. It can be really harmful to humans and to dogs, it only takes a teaspoon of the toxin to kill a dog,” Emily said.

Is it always dangerous to swim at Coes Ford?

Cyanobacteria isn’t always present at Coes Ford – usually appearing during periods of extended hot weather, in combination with low river flow and enough nutrients.

It is important to get a dog to the vet as soon as possible if it comes into contact with cyanobacteria.

“Toxic algae risk is reported on Environment Canterbury’s website, on the Community Public Health website, and on LAWA – which is your best bet for water quality, in terms of E. coli as well as cyanobacteria for 100 popular swimming sites around the region,” she said.

Once samples are collected for the pilot study, the data and samples are tested and processed by ESR in the laboratory.

It is hoped that the results of the pilot study will be used to inform a larger more intensive investigation to review New Zealand’s swimming water quality monitoring and reporting guidelines.

Further information on what’s being done to address water quality.