The water along the shore line of the Fukushima Daiichi nuclear power plant has high levels of iodine-131.

Nuclear and Industrial Safety Agency said that iodine 131 in excess of 1,250 times regulated standards was found in the ocean 330 meters (1082.68 feet) south of a plant water outlet on Friday.

Iodine-131 has a short half life span of 8 days (radioactive strength reduced by half within 8 days).  It is the product of nuclear fission.  Finding so much iodine-131 in the ocean near the nuclear plant, is another indicator that the reactor cores are leaking.