People attend a rally protesting against Japan's dumping of nuclear-contaminated wastewater into the ocean in Busan, South Korea, on Aug. 26, 2023. (Xinhua/Lu Rui)

Thousands of South Korean fishermen, activists and politicians held a protest rally in central Seoul on Saturday, condemning Japan's dumping of nuclear-contaminated wastewater into the ocean.

The participants shouted "Immediately stop dumping radioactive wastewater into the ocean" and "Japan must store nuclear-contaminated wastewater on its soil," urging the South Korean government to file a lawsuit with the International Tribunal against the Japanese government.

The rally came after Japan started discharging the first batch of radioactive wastewater from the crippled Fukushima Daiichi nuclear power plant on Thursday.

"Even if fishermen catch blue crabs, merchants do not take them even after their price plunged by more than half. Wholesale marine products markets (in Seoul, Busan and other cities) are seeing business slack," Kim Young-bok, a 63-year-old fisherman from the southwest coastal county of Yeonggwang, said during the rally.

Kim said Japanese Prime Minister Fumio Kishida, who was committing crimes against humanity, should immediately stop the wastewater discharge that would bring catastrophe to all humankind around the world.

Standing beside his mother, an eight-year-old boy said he could not understand why Japan dumped the wastewater into the ocean shared by other countries, while a 10-year-old girl said she could not go for a swim in the sea due to the marine dumping.

"I feel very sorry for South Korean people because Japan, where I was born, dumped radioactive wastewater into the ocean," said Yuji Hosaka, a professor at Sejong University in Seoul.

Hosaka urged Tokyo to opt for other approaches, such as storing the wastewater in large water tanks for more than 100 years, which was proposed in 2017 but ignored by the Japanese government.

"If it's safe and unproblematic, why would Japan not store (the wastewater) on its land but dump it into the Pacific Ocean, the well of the world, to worry everyone and damage everyone's health?" said Lee Jae-myung, leader of the main opposition Democratic Party.

Lee called the wastewater dumping a "provocation against humanity" and a "declaration of war" against all countries around the Pacific Ocean, urging Tokyo to immediately stop the discharge threatening the safety of people around the world.

Following the one-and-a-half-hour rally, the protesters marched about 5 km in downtown Seoul to the presidential office, holding leaflets printed with "Retract the dumping of Fukushima nuclear-contaminated wastewater."

Struck by a massive earthquake and an ensuing tsunami in March 2011, the Fukushima nuclear power plant suffered core meltdowns. It generated a massive amount of water tainted with radioactive substances from cooling down the nuclear fuel.