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How do you test water quality?

Central Otago students are learning how to test water quality in their local rivers.


Year 8 students at St Gerard’s School in Alexandra are learning how to monitor the water quality of their local rivers and streams in an effort to understand why some freshwater spots are not swimmable.

Checking PH

“We’ve been looking at the temperature of the water, how clear it is, and what bugs live there,” 12-year-old Olly Lyon explains.

The students have also looked at the PH level to see how acidic the river is and the conductivity to get an idea of how contaminated it might be.

When asked what conductivity is, the students explain that measuring how easily electricity passes through the water can shed light on the concentration of minerals and nutrients dissolved in it.

A high reading means high concentrations, from either natural sources like soil and rain or from manmade sources like farmland runoff carrying livestock poo, fertilisers or pesticides into the river.

If concentrations are too high, this can lead to river health problems such as too much algae. When algae flourishes, it can create river conditions that harm fish – and too much of a specific kind of algae makes the water unsafe for us too.


At the four river sites the students are monitoring – Alexandra, Galloway, Omakau and Becks – the water quality is very similar in some ways but differs dramatically in others.

“I liked looking at the bugs and I think my favourite are the boatmen because they go really fast,” says Hannah Tait, 12.

“We’ve found lots of mayflies, but Becks has loads of different kinds of bugs, which means it is a very healthy habitat for lots of species to live in.”

Omakau is a different story, the team tells us. They did not find any insects and noticed that the weeds were overgrown on the river banks.

Across all of the rivers, however, the students have found that the temperature remains at around 18 degrees Celsius and that the acidity is healthy at between 6.5 and 7.5 PH level.

“I liked looking at all the data and comparing the different numbers we have for each area,” 12-year-old Emma Kelliher says.

Pouring water

Surprisingly, the conductivity is not as high as the students expected – making them wonder what might be causing the big difference in weed growth and insect numbers between Becks and Omakau.

“Omakau is now green and disgusting – and the weeds are even bigger than me!” says Tessa Handford, 12, who leads the river monitoring group.

The students think the most likely explanation is that the site at Becks has a lot more shade covering the river, which means more bugs can survive. This year they are investigating whether this is true or not.

group working together

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Photo credits: Tessa Handford and Jeremy Hogue.

About the project

St Gerard's Logo This project is being supported by funding from the Otago Participatory Science Platform (PSP), which is managed by Craig Grant at Otago Museum.


Scientists and locals collaborating around a table

Participatory Science Platform

The Participatory Science Platform supports collaborative projects that bring together communities and scientists or technologists on research investigating a locally-important question or problem.

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