Radiation from the 2011 Fukushima nuclear disaster in Japan has been detected at an increased number of sites off U.S. shores, including the highest level in the area detected to date, scientists announced Thursday. While the levels are still too low to be considered a threat to human or marine life by the government's standards, tests of hundreds of samples of Pacific Ocean water reveal that the Fukushima Daiichi plant has continued to leak radioactive isotopes more than four years after the meltdown—and must not be dismissed, according to Woods Hole Oceanographic Institution (WHOI) marine radiochemist Ken Buesseler.