A sharp rise in the radioactivity of seawater off the coast of Japan may signal a new leak at the Fukushima Daiichi plant. The rise in radiation levels was announced after a magnitude-5.9 earthquake shook Japan early Saturday morning, and officials told the country's nuclear plant operators to beef up their quake preparedness. There were no reports of damage from the quake, and no danger of another tsunami. Since the tsunami that plunged the Fukushima reactor into crisis, emergency workers have been spraying the reactor with massive volumes of seawater to try to keep it cool. Some of the water has leaked back into the Pacific, though workers closed the leak and radiation levels in the ocean dropped. Now, the radioactivity levels are back up to 6,500 times the legal limit—possibly the result of new steel panel installations at the plant on Friday that could have stirred up radioactive waste.