Transcript for Is Japan's Fukushima Power Plant Still a Threat?
We've come to one of the most toxic places on the planet. There's always going to be doing it is. Have a -- To get a rare look inside the species -- ground zero. Workers here are racing to contain the damage after that massive tsunami triggered one of the worst nuclear disasters in history. But what if mother nature strikes again. During our trip a typhoon made land fall near Fukushima. Didn't. -- The plant's operator teppco assures the world that time -- Kansas. Disaster -- beefed up defenses with new technology that will insure backup power and supply water to cool reactors during an emergency. But how will nature fare against the threat from Fukushima. This summer the company admitted that even after the accident radioactive water had seeped into the ocean. And many scientists fear the plant still leaks everyday. But how bad -- damage to find out -- venturing to deceased surrounding the power plants. Along with us a team of maverick Japanese scientists led by radiation expert doctor -- and so -- -- -- plus at all. Our rented fishing boat transformed into a mobile -- -- can detect radiation in the water and the ocean floor. You can't -- working. About a half a football field away eventually. This is as close as we can -- to collect samples without -- Her mission as the radiation detectors -- The -- has to work quickly to limit our exposure -- -- A lower this device. Down into the ocean. Measuring the water -- -- how much contamination. There is. -- just behind the plant. There are more than 1000. Temporary tanks holding over 100 million gallons of highly radioactive waste water -- Critics say the tanks are poorly constructed. And -- to admit some of them have -- Absolutely. Doctor -- wants to measure the full extent of the damage. He doesn't take long for the team says it finds evidence of radiation a lot of -- and you just now. He says it's just what he suspected. Even though the radiation levels he says he measured fall within the legal limit for swimming in drinking. They are still -- 1000 times higher than for the meltdown. And the effects of long term exposure for people and the environments are still unknown. Kid dammit it's been done be -- here is it too -- It's not too late this as much pain can't do it alone won't yeah we need help from the rest of the world. We've seen -- to -- -- is trying to stop leaks trying to decontaminated just not working. Not far from the power plant we -- American oceanography for Ken batchelor. He's -- radiation expert who study the fallout from the world's largest nuclear disaster in Chernobyl 26 years ago. And now he's come here to help survey the damage. Never had this -- activity released accidentally into the ocean. So now the question how long it would take to -- -- from the land to the ocean in the power plants into the sea life. And across the Pacific. The government claims radiation from Fukushima is contained in this small harbor outside the planting. But on expeditions into the Pacific. Bestseller and this team of scientists say they measured radiation linked to Fukushima more than seventy miles away. Some of that radiation is predicted to reach American shores early this year the levels are expected to be very low. I think the fear of what's happening outside the local area. It's been exaggerated for America's story -- -- and our beaches mountains revenues I think is overblown. What does concern him. How this unprecedented amount of migrating radiation will affect the food chain basically try to get as much -- is possible. -- says some fish they caught near the power plant tested positive for radiation. Levels low enough to make them legally safe to eat. But in that. These have tested dangerously high to the Japanese government isn't taking any chances -- -- colts are on the line. This one of the countries that consumes the most fish in the world. And now they've got to convince everyone here and -- -- -- that these kids are safe to eat. Even fish -- miles outside of Fukushima are inspected before they can be sold at market. They're required to test every batch. Trace amounts of radiation linked to the power plants have been detected in bluefin tuna as far away as California. Still experts say Americans shouldn't worry dangerous radiation -- -- as -- fish migrate to the US. To end our trip we visit -- headquarters in Tokyo. A spokesman for this embattled company assures us -- will keep testing the -- surrounding the plant. And publicly report the results because the Fukushima daiichi power plant -- Any kind of threat to the public today. -- festival he says people can feel safe. There is no threat to the general public -- Why should the public trust -- now let us -- the only way to restore trust he tells me. He's to continue decommissioning the plant safely and explain the process to the public but a pleasant thing. Our journey may be over -- back. -- the cleanup goes on. Closing at Fukushima Dai Ichi power plant will cost an estimated eighteen million dollars. And take forty years to complete. And then there's the damage we can't sleep radiation on land and in the ocean. -- -- -- invisible enemy for generations. For Nightline I'm Cecilia Vega in Fukushima Japan.
This transcript has been automatically generated and may not be 100% accurate.