Asahi: Radioactive cesium spread 600 km in waters off Fukushima
"...scientists said, in amounts that reached 100 times pre-accident levels."
Fukushima nuclear pollution in sea was world's worst: French institute. Japan Today Oct. 28, 2011 - http://www.japantoday.com/category/national/view/fukushima-nuclear-pollution-in-sea-was-worlds-worst-french-institute
Ken Buesseler, a scientist at Massachusetts’s Woods Hole Oceanographic Institution, told the paper that Fukushima was by far the largest accidental release of radioactive material into ocean waters—exceeding, by a magnitude of 100, the Chernobyl contamination of the Black Sea. (cited in Alex Roslin http://www.straight.com/article-491941/vancouver/what-are-officials-hiding-about-fukushima?page=0%2C2)
Some background on Cesium Reporting in Japan
Fukushima Diary Reported 4/15/2012 that the Japanese Ministry of Education, Culture, Sports, Science and Technology (MEXT) admitted that their monitoring data of sea water and ground near Fukushima were inaccurate, reporting 20% lower than actual http://fukushima-diary.com/2012/04/mext-showed-the-contamination-level-lower-than-actual-by-20/