In the past three months he has filled 466 huge bin bags with plastic bottles.
Bence Pardy spent his summers as a child by Hungary's second main river, the Tisza. Now, at 32, he has given up his job to move back there permanently to collect plastic waste which pollutes its waters.
The Tisza, one of the main rivers in eastern Europe, starts in Ukraine and flows across Hungary to join the Danube in Serbia. It then flows eastwards to empty into the Black Sea.
Over the past three months, working all day on his own from a small motorboat, Pardy has collected by hand plastic bottles from the river and its floodplains to fill 466 huge binbags.
In many places there are floating waste islands made up of plastic bottles already overgrown with lush vegetation.
"We used to have a house in a nearby small village and came here for the summers. There was no waste at that time... there wasn't this craze for plastic plates and forks," Pardy said, picking empty bottles and plastic bags from the grass and trees hanging over the slow-moving river.
He worked as a waiter in Budapest before he moved to Tiszafured, a town nearby, and now lives in a small caravan. As his money was running out, he launched a social media campaign to raise funds for the project.
During another large-scale initiative, which he also joined, volunteers removed more than 11 tonnes of waste from the Tisza this summer, Pardy said.
The waste, which also includes refrigerators, car parts and even hazardous items such as needles, is mostly washed downstream from Ukraine during flooding from the waste dumps there, he said.
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"I was so shocked by this that I could not continue doing and enjoying my job and now here I am," said Pardy.
"My sad experience is that I see anglers or the people who come for holidays and they just walk past the rubbish, and even when it is at arm's length, they don't pick it from the river. I am astonished to see such negligence."
Pardy said he was determined to continue what he started.
"We are getting all the warning signs, and we still do not want to change. I think we are heading into an abyss at high speed... We believe we can separate ourselves from nature, and that our actions have no consequences."
"I am trying to be an optimist, and yes, there are all kinds of efforts, but this is still way too little."