IWAKI, Japan  - Fishing communities in Japan are alarmed over the decision to release contaminated water stored at the wrecked Fukushima Daiichi nuclear plant, a move that has also set off a diplomatic ruckus with neighbours China and South Korea.

Japan's government said on Tuesday it will release more than 1 million tonnes of treated water from the Fukushima site in stages starting in about two years. China called the decision "extremely irresponsible", while South Korea said it will explore petitioning an international court to stop the release.

The still-struggling fishing communities of northern Japan, devastated by the earthquake and tsunami that caused the meltdowns at Fukushima 10 years ago, have long expected the decision and have lodged regular protests with the government.

"The thing I'm most afraid of is the damaging rumours even if fish are declared safe," Masao Takahagi, 67, told Reuters.

Still, checking nets on his boat with his wife at Onahama port in Iwaki city, 60 km (35 miles) south of the Fukushima site, he wasn't sure there was much he could do about it.

"In the end, there's only the sea," he said.

Although the government considered other options, most experts had expected it to eventually opt for release into the Pacific Ocean after the water is treated and diluted to within regulatory limits.

Fishing communities and others suffering reputational harm from the release will be compensated, Tokyo Electric Power, owner of the Fukushima station, said.

Catches from waters near the plant are tested for radiation, as the meltdown spread huge amounts of radioactive material over air, land and sea.

Most restrictions on fishing have been lifted, though, said Hiromi Matsubara, 60, as he stepped into the cockpit of his boat at Onahama.

"We have just started to return to full-scale operations. If the water is released, I'm afraid that we will go back to where we were," he said.

Others seemed just as resigned.

"The government has said releasing the water is scientifically safe," said Motonobu Kimura, a 38-year-old trader sorting fish at the port.

"The only thing we can do is to trust them and do business with those who will do business with us."

(Reporting by Akira Tomoshige in Iwaki, Japan; Writing by Rikako Maruyama and Aaron Sheldrick in Tokyo; Editing by Tom Hogue) ((aaron.sheldrick@thomsonreuters.com; 81-80-2677-4134;))