to the sea by surface water crossing contaminated soil. The possible presence of other radioactive substances, such as strontium-90 or plutonium, has not been sufficiently studied. Recent measurements show persistent contamination of some marine species (mostly fish) caught along the Fukushima coast. Migratory pelagic species are highly effective and rapid transporters of radioactivity throughout the ocean. Elevated levels of caesium-134 appeared in migratory species off the coast of California that were not seen pre-Fukushima. Scientists have also discovered increased traces of radioactive isotope Caesium-137 in wine grown in a vineyard in Napa Valley, California. The trace-level radioactivity was in dust blown across the Pacific Ocean. As of March 2012, no cases of radiation-related ailments had been reported. Experts cautioned that data was insufficient to allow conclusions on health impacts. Michiaki Kai, professor of radiation protection at Oita University of Nursing and Health Sciences, stated, "If the current radiation dose estimates are correct, (cancer-related deaths) likely won't increase." In August 2012, researchers found that 10,000 nearby residents had been exposed to less than 1 millisievert of radiation, significantly less than Chernobyl residents. As of October 2012, radioactivity was still leaking into the ocean. Fishing in the waters around the site was still prohibited, and the levels of radioactive 134Cs and 137Cs in the fish caught were not lower than immediately after the disaster. On 26 October 2012, TEPCO admitted that it could not stop radioactive material entering the ocean, although emission rates had stabilized. Undetected leaks could not be ruled out, because the reactor basements remained flooded. The company was building a 2,400-foot-long steel and concrete wall between the site and the ocean, reaching below ground, but it would not be finished before mid-2014. Around August 2012 two greenling were caught close to shore. They contained more than 25,000 becquerels (0.67 millicuries) of caesium-137 per kilogram (), the highest measured since the disaster and 250 times the government's safety limit. On 22 July 2013, it was revealed by TEPCO that the plant continued to leak radioactive water into the Pacific Ocean, something long suspected by local fishermen and independent investigators. TEPCO had previously denied that this was happening. Japanese Prime Minister Shinzō Abe ordered the government to step in. On 20 August, in a further incident, it was announced that of heavily contaminated water had leaked from a storage tank, approximately the same amount of water as one eighth (1/8) of