Apparently the International Atomic Energy Agency believes it to be safe, but the (demsoc) Communist Party of Japan are also opposed to the release

In a disturbing coincidence, the first death from the hydrogen bomb was a Japanese person.

It's because the Fukushima meltdown released 8-45 PBq (quadrillion becquerels) of just cesium-137 into the ocean, and global nuclear testing has released a total of 400 PBq. The current radioactive release at Fukushima Daiichi is 22 TBq (trillion becquerels) of tritium per year, a thousandth as much as the meltdown itself. Some active power plants actually release more than this. The seawater being released is diluted to 1,500 Bq per liter compared to the WHO drinking water standards of 10,000 Bq/L or less and the Japanese release limit of 60,000 Bq/L. However, there was a leak recently that brought it up to that Japanese limit. If that was drinking water and you drank two liters of it every day, you'd be as irradiated as a flight attendant. That is to say, they should keep it lower. However, don't expect three-eyed fish from the radiation - that stuff is more likely from toxic chemicals.