She recounted some of her experiences to the students with the animals and rubbish in the water, such as a manta ray with rope wrapped around it, and how plastic bags look like jellyfish to turtles.
"You have the power to make it better," Ms Bowles said.
"Every single piece of plastic made in the last 60 years is still here."
She taught the students about nurdles.
"A plastic nurdle is what people order if they want to make something out of plastic."
They are very small - the size of stones and sometimes get spilt into the sea and wash up on beaches.
She is targeting children because she feels the message is more powerful coming from them than adults.
In return, Ngunguru School played the video of their Choose to Refuse song, which they recorded as part of their work to go plastic free.
Ms Bowles said while teaching her students all about ocean conservation in the UK, one said to her: "If you love the sea and you're always telling us we can make a difference, why are you still in the classroom?"
She decided to build a bike out of bamboo and pedal it around the world saying no to single use plastic.
Ms Bowles made the bike, which weighs 17.5kgs, at a bamboo bicycle club in London.
"It [bamboo] was really fun to work with. When I've finished using it as a bike, I can put it in the compost."
It has a dynamo on the front wheel which creates electricity to power her light and charge her phone.
Ms Bowles started her trip on November 20 and leaves from Queenstown in April. She plans to cycle all over the country, talking to schools and other groups about plastic.
There is a growing global movement to stop the use of single-use plastic bags.
