Radioactive contamination of seawater has often caused concern, for example about releases from Sellafield and Le Havre and later about the Fukushima disaster. Repeated reporting has contributed to the general feeling that the sea is particularly sensitive to radioactive contamination (Greenpeace,1998). This is not the case, it is rather the opposite. Marine life is much better protected against radioactive contamination than life on land. This protection is due to three natural factors: shielding, dilution and isotope competition.