No, its just plain, normal fear. Your connecting the Japanese tsunami to similar situations, in example when your by the sea, you usually think of things connected to that event, eg Fun, Friends, Fish, Drowning. It seems that you were a bit disturbed by what had happened in Japan. But there is no worries this is very natural, not a phobia or anything unless your scared of the sea water, which your not. So I'd say just have fun, you never know what will happen.