Authorities have insisted the radioactivity will dissipate and poses no immediate threat to sea creatures or people who might eat them. Most experts agree.
Regardless, plant workers on Saturday began dumping sandbags filled with zeolite, a mineral that absorbs radioactive cesium, into the sea to combat the radiation leaks.
The rising radiation announcement came after another large aftershock rattled Japan Saturday morning.
There were no reports of damage from the magnitude-5.9 earthquake, and there was no risk of a tsunami similar to the one that struck the Fukushima Dai-ichi plant March 11 after a magnitude-9.0 earthquake, causing Japan's worst-ever nuclear plant disaster.
Since the tsunami knocked out the plant's cooling systems, workers have been spraying massive amounts of water on the overheated reactors. Some of that water, contaminated with radiation, leaked into the Pacific. Plant officials said they plugged that leak on April 5 and radiation levels in the sea dropped.
Also Saturday, Japan's nuclear safety agency ordered 13 nuclear power plant operators, including the owner of the Fukushima nuclear plant, to improve earthquake preparedness at their plants.
There was also a report that TEPCO, the company that owns the damaged Fukushima plant, may be dismantled.
That's according to un-named sources in the Japanese newspaper, Asahi Shimbun.
The report states there is a secret government plan to put the company into bankruptcy and restructure its assets.
The Associated Press contributed to this report.