TOKYO (AP) — Levels of radioactive materials have risen sharply again in seawater near the troubled Fukushima Daiichi nuclear plant in northern Japan, raising the possibility of new leaks at the complex, the government said Saturday.

Workers have been struggling to deal with contaminated runoff at the plant that resulted from makeshift efforts to cool reactors and spent fuel rod pools after a huge earthquake and tsunami knocked out regular cooling systems.

Much of the tons of water that has been sprayed on the reactors and pools has been stored, but the company that operates the plant, the Tokyo Electric Power Company, recently discovered and eventually plugged a leak that could have been gushing for days. The levels of radioactive materials in the ocean near the plant dropped after that.