Japan’s environment minister says contaminated water from the Fukushima nuclear plant may have to be released into the ocean because storage space will run out in 2022.
More than a million tonnes of water that has been used to cool melted reactors is kept in giant tanks.
Fisherman’s groups are strongly opposed to the idea but many scientists say it would pose a low risk.
The government said a final decision had not yet been taken.
Reactor buildings at the Fukushima power plant were damaged by hydrogen explosions caused by the earthquake and tsunami in 2011. Three reactors melted down.
The Japanese government decided that the area would be cleaned in a vast operation which will take many decades to complete.