The Tokyo Electric Power Company, or TEPCO, says a large amount of groundwater may be entering the crippled Fukushima Daiichi nuclear power plant.
TEPCO says it has found that 200 to 500 tons of what is probably rainwater that seeped into soil may be entering daily through cracks in walls into the basements of buildings housing reactors and turbines.
The utility says it's worried that this will increase the amount of highly radioactive water in the basements.
Workers at the plant are injecting about 550 tons of water a day to cool 3 of its damaged reactors. About 80,000 tons of highly radioactive water has already accumulated in the buildings.
TEPCO says it plans to keep levels of radioactive water lower than those of groundwater to stop further inflows.
The government's Nuclear Safety Agency says groundwater inflow must be considered in drawing up a long-term decontamination plan.