Japan's fisheries federation chief has reiterated his demand that the government ensure safety and dispel reputational damage in releasing treated and diluted water from the Fukushima Daiichi nuclear plant into the ocean.

The head of the National Federation of Fisheries Co-operative Associations, Sakamoto Masanobu, issued a statement on Tuesday following the government's decision to start the release on Thursday if conditions are right.

Sakamoto said he remains opposed to the planned release without the understanding of fishers and the public. But he added that it is a fact that understanding of the plan's safety from a scientific aspect has deepened through the IAEA report and briefings to fishers.

Nonetheless, Sakamoto noted that scientific safety and the public's peace of mind are different matters, and that scientific safety alone will not dispel reputational damage.

Prime Minister Kishida Fumio has said the government will support the fishers and continue offering necessary measures, and take full responsibility for the discharge even if it takes several decades to complete.

Sakamoto said he strongly urges the government to faithfully uphold Kishida's promise so that fishers in Fukushima and other prefectures will have an environment where they can continue their business for generations to come.

The Fukushima Daiichi nuclear plant suffered a triple meltdown following the March 2011 quake and tsunami. Water used to cool molten fuel at the plant mixes with rain and groundwater.

The accumulated water is treated to remove most radioactive substances, but still contains tritium.

The government plans to dilute the treated water to reduce tritium levels to about one-seventh the World Health Organization's guidelines for drinking water quality before releasing it into the sea.