TOKYO — Japan’s government decided Tuesday to start releasing treated radioactive water from the wrecked Fukushima nuclear plant into the Pacific Ocean in two years — an option fiercely opposed by fishermen, residents and Japan’s neighbors.

The decision, long speculated but delayed for years due to safety concerns and protests, came at a meeting of Cabinet ministers who endorsed the ocean release as the best option.

The accumulating water has been stored in tanks at the Fukushima Daiichi plant since 2011, when a massive earthquake and tsunami damaged its reactors and their cooling water became contaminated and began leaking. The plant’s storage capacity will be full late next year.

Prime Minister Yoshihide Suga said ocean release was the most realistic option and that disposing the water is unavoidable for the decommissioning of the Fukushima plant, which is expected to take decades. He also pledged the government would work to ensure the safety of the water and to prevent damaging rumors on local agriculture, fisheries and tourism.

The plant’s operator, Tokyo Electric Power Co., and government officials say tritium, which is not harmful in small amounts, cannot be removed from the water, but all other selected radionuclides can be reduced to levels allowed for release.

Some scientists say the long-term impact on marine life from low-dose exposure to such large volumes of water is unknown. The government stresses the safety of the water by calling it “treated” not “radioactive” even though radionuclides can only be reduced to disposable levels, not to zero.

The amount of radioactive materials that would remain in the water is also still unknown. Under the basic plan adopted Tuesday by the ministers, TEPCO will start releasing the water in about two years after building a facility and compiling release plans adhering to safety requirements.