The students at Te Kāpehu Whetū are often tempted to cool off in the Hātea River when it's hot outside.

But there's a problem - it's dirty.

So when a group of girls from Te Kāpehu Whetū were asked to choose a topic to focus on for a STEM (Science Technology Engineering and Mathematics) project, they chose water quality.

"In summer we really like swimming and our school is right by the river so it's tempting. But it's paru," student Makayla Panapa said.

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As part if the project the girls built, developed, and coded three devices which can measure the river's temperature, turbidity (clarity) and the water's ability to conduct electricity which is a test for how clean it is - for example pure water is not a good conductor of electricity.

Martin Knoche, chief executive of the Northland Innovation Centre, said Te Kāpehu Whetū STEM teacher Chipo Fumhanda approached him about doing a project in May but said the girls have driven it.

"The whole objective was exposing them to technology," Knoche said.

"There are over 2000 IT jobs not being filled, so there's a talent gap and often girls think technology is too complicated.

"I think what we've done is demystified technology and now they're hopefully confident they can do technology stuff."

The girls designed the new electronic sensors, soldered the components on to a board, and wrote the software to control the device.

They had help with coding from TechnoHackers and help designing and building the device from CruzPro.

Before the most recent school holidays the girls placed the water-quality sensors in three different places - Pipiwai Rd, which is a source of the river; Mair Park; and in the Whangārei Marina.

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The data was saved to a micro-SD storage card in each device and after two weeks they pulled the sensors up and analysed the data using code they had written.

It was no surprise to the girls to find the water in the marina was the dirtiest.

"It looks ugly. It's by our school so we're trying to make our area look a bit pretty. It's like this nice walk next to disgusting river," said Amelia Fenton Phillips.

On Friday the girls talked to Whangārei mayor Sheryl Mai about their project and presented the results. She invited them to share their data at a council meeting.

The girls said they were pretty impressed with what they had achieved and now want to expand the project and focus on improving the water quality.