Japan released treated wastewater from the Fukushima nuclear disaster into the ocean. Experts say it's safe, but one would avoid the fish.

• Japan said it plans to release 1 million metric tons of treated radioactive water into the Pacific.
• Neighboring countries, fisheries, and local groups object, fearing it could harm sea life and more.

Japan started releasing treated, but still radioactive water into the Pacific Ocean on Thursday.

The water is from its Fukushima nuclear power plant that, in 2011, underwent a meltdown and is considered one of the biggest nuclear tragedies in history.

Local authorities suggest that it may take up to 40 years to complete the decommissioning process.

One primary step in that process is to remove the roughly 1,000 water-filled tanks that cover much of the plant's grounds. The tanks contain water that was used to cool the three damaged reactors.

After the 2011 disaster, the radioactive water leaked into the plant's basements where it was collected and later stored in tanks.

But Japan said the tanks will reach their capacity limit of 1.37 million metric tons by 2024.

So the country has set its sites on the Pacific Ocean as a final resting place where TEPCO, the plant's operator, plans to release 1 million metric tons over the next 30 years. That's enough to fill 500 Olympic swimming pools.

IAEA Director General Rafael Mariano Grossi has said, "The controlled, gradual discharges of the treated water to the sea, as currently planned and assessed by Tokyo Electric Power, would have a negligible radiological impact on people and the environment."

Nuclear experts Insider spoke with agree the risk of radioactive poisoning or other harmful effects from the water's release is minimal.

Why treated radioactive water is 'quite safe'

This isn't the first time humans have released water from nuclear plants into a larger body of water.

"Many nuclear facilities are allowed to discharge slightly radioactive water. Such discharges are at very low levels of radioactivity and are considered to be quite safe," Kathryn Higley, a distinguished professor of nuclear science at Oregon State University, told Insider.

As long as the water's radioactive levels are below a certain limit, it is considered safe to release them. And "the limits are well known," Aldo Bonasera, a senior scientist and nuclear physics expert at Texas A&M University's Cyclotron Institute, told Insider.

The water Japan is releasing is expected to contain about 190 becquerels — a measurement of radioactivity — of the radioactive element tritium.

That's significantly lower than the maximum limit for drinking water — 10,000 becquerels per liter — recommended by the World Health Organization, and lower than the US limit of 740 becquerels per liter.

"The water from the Fukushima plant has been treated so that it is less radioactive than what is allowed in drinking water in many countries," Higley added. "So yes it is radioactive but only slightly and it is not harmful."

Japan's neighbors say it's a bad idea

Not everyone is ready to believe in Japan's safety claims. Among its neighbors, the country that appears most concerned is China.

In a press conference on Tuesday, Chinese foreign ministry spokesperson Wang Wenbin said, "The ocean sustains humanity. It is not a sewer for Japan's nuclear-contaminated water."

He said that Japan hasn't resolved global concerns about the purification facility's reliability long-term, the accuracy of its radioactive water data, and monitoring measures.

"This is extremely selfish and irresponsible, as the discharge will spread the risks of nuclear contamination to the rest of the world," Wenbin added.

But nuclear experts say that risk is low.

"Many different organizations have looked at the proposed discharge actions and have agreed that this is the best course of action. I believe that this is environmentally the safest approach," Higley said.

Hong Kong is also opposing Japan's water discharge plans and aims to ban seafood imports from nearly a dozen Japanese prefectures. Russia has also expressed serious concern in the past.

On the other hand, the Korean government stated, "There are no scientific or technical problems with the plan to release the contaminated water."

That said, South Korea has banned Japanese seafood imports from areas near Fukushima since 2013 and said it will continue doing so.

Is the fish in the discharge zone safe to eat?

Apart from countries, many fishing companies, coastal communities, and organizations whose business depends on marine life in the Pacific have criticized Japan.

They believe that this decision could ruin their livelihood as many countries and food companies may refuse to buy fish and other resources obtained from possibly radioactive water.

Some environmental organizations are also supporting the fishing community.

Greenpeace said in a statement: "The decision disregards scientific evidence, violates the human rights of communities in Japan, and the Pacific region, and is non-compliant with international maritime law. More importantly, it ignores its people's concerns, including fishermen."

While addressing these concerns, the Japanese government ensured that it would regularly monitor the water and fish quality in the discharge zone.

When it comes to eating the fish, however, experts were torn.

"The level of radioactivity has been reviewed by multiple organizations to ensure that it is consistent with international practices," Higley said. "It is my opinion that it is safe. It is safe to eat the fish."

But Bonasera said he would err on the side of caution.

"Fish moves over large distances, and to my knowledge, some fish captured in California contained some radioactivity produced in the Fukushima reactor," Bonasera told Insider.

It's worth noting here that what scientists measured in fish off the US West Coast were radionuclides of cesium 134Cs and 137Cs, not tritium. Of the two, 137 Cs is considered more dangerous and may increase cancer risk if ingested.

So, the fear of anything even related to radioactive elements in the ocean is real.

"No matter what the authorities will do, the public — including myself — may avoid products coming from the Fukushima region," Bonasera added.