Japan’s plan is to dispose more than one million tonnes of treated radioactive water into the Pacific Ocean next year.
International Observers are visiting its Fukushima plant to find out if that’s safe.
More than a decade ago, a powerful earthquake and tsunami hit Japan, killing thousands of people.
It also led to one of the world’s worst nuclear disasters when it damaged the Fukushima power plant.
More than a million tonnes of treated radioactive water have been stored in tanks at the site, but they are soon set to fill up.
Japan has said the best way forward is to dump some of the water into the Pacific Ocean, starting next year.
To make sure the plan meets international standards, Japan got help from the International Atomic Energy Agency, an independent organisation.
This week, a team of about 15 observers are visiting the plant to assess the plan.
“They will be there to ensure that the plans are being done to the specifications that they had promised,” said Dr Patrick Burr, a nuclear engineering expert at the University of New South Wales.
“They’ll be there to be, in a way, sort of a watchdog reassurance to the international community that things are being done properly and strictly to within the regulations.”
The water is treated in a filtration process, which Dr Burr says removes most of the radioactive particles.
Dr Burr said the filtered water is so safe, humans could drink it.
But some have raised concern, with The Pacific Conference of Churches General Secretary Reverend James Bhagwan saying he welcomes the observers’ visit, but has problems with Japan’s plans.
“If it’s safe, then keep it where it is,” he said.
“Why do they have to dump it in the Pacific Ocean really is our question. The Pacific Ocean is alive, it is the home for so many species,” he added.
“It is so important in terms of the creation of oxygen for the planet, not just for our region.”
He is calling on Japan to halt its plans.
The ABC has contacted the IAEA for comment.