Previously-Secret 1955 Government Report:Ocean May Not Adequately Dilute Radiation Nuclear Accidents

The entire page is worth a read. esp. halfway down where there is an animated graphic
which shows the projected dispersion of debris from Japan.

and the last paragraph is really important:
" According to a previously secret 1955 memo from the U.S. Atomic Energy Commission regarding concerns of the British government over contaminated tuna, “dissipation of radioactive fall-out in ocean waters is not a gradual spreading out of the activity from the region with the highest concentration to uncontaminated regions, but that in all probability the process results in scattered pockets and streams of higher radioactive materials in the Pacific.
We can speculate that tuna which now show radioactivity from ingested materials (this is in 1955, not today)]have been living, in or have passed through, such pockets; or have been feeding on plant and animal life which has been exposed in those areas.”

Because of the huge amounts of radioactive water Tepco is dumping into the Pacific Ocean, and the fact that the current pushes water from Japan to the West Coast of North America, at least some of these radioactive “streams” or “hot spots” will likely end up impacting the West Coast.
http://www.washingtonsblog.com/2012/06/why-the-ocean-may-not-adequately-dilute-the-radiation-from-fukushima.html