Tokyo Electric Power Co. plans to release 3,000 tons of lightly radioactive water into the ocean from the Fukushima Daini nuclear complex, the sister plant of the stricken Fukushima Daiichi complex, officials said Wednesday.

The utility, also known as Tepco, is going ahead with the discharge even as the fishing industry complains it will add to worries about the contamination of seawater and further reduce fish consumption in Japan .

The water is believed to be largely within permissible levels of contamination for discharging into the ocean. But Tepco and the government want to avoid the kind of backlash from local fishery associations and neighboring countries that followed the discharge of far more toxic water from the Daiichi plant in April.

The seawater at the Daini plant, located 10 kilometers (six miles) south of the Daiichi complex, entered when the plant was flooded by the massive March 11 tsunami. While the tsunami knocked out power at the Daiichi plant, causing a meltdown of some of its reactor cores, the Daini complex was safely shut down after the disaster.

Tepco says the water has accumulated in reactor and turbine buildings, as well as other facilities, raising concerns that it might corrode piping and cause leakage of radioactive materials.

The government's Nuclear and Industrial Safety Agency, which hasn't yet decided whether to approve the plan, said the water contains a small amount of radioactive material, including manganese-54 and cobalt-58. But the amounts are mostly within permissible levels for discharge into the ocean. NISA said there is an estimated 3 billion becquerels of radioactive materials in the 3,000 tons of water. By comparison, in the first week of April, 520 tons of highly radioactive water leaked from the Daiichi complex containing 4,700 terabequerels.

The water will undergo a decontamination process at Daini to further reduce the levels of radioactive material before being released into the ocean, Tepco said.

Tepco has sounded out government agencies and local governments on the plan. But the Fisheries Agency and some local governments are likely to oppose it, regardless of how low the levels of radioactive materials.

"Why does Tepco have to do this when the fishing industry is struggling with rumors of radiation contamination?" asked one fisheries-agency official. "It is not the issue of how low the radiation is. Such a move will reinforce fears of seawater contamination and further put off consumers from buying fish."

Demand for fish caught in the prefectures of Fukushima and neighboring Ibaraki took a hit after sandlance fish caught in April were found with more than allowable levels of radioactive iodine and cesium. Agency officials said sales of fish have been slow even outside these prefectures.

"Tepco should consult the relevant parties before implementing the plan, even if it would be perfectly legal to go ahead with it," NISA spokesman Hidehiko Nishiyama said.

NISA's caution may be a product of the uproar among neighboring countries and the local fishing community when Tepco dumped 10,000 tons of low-level radioactive water in mid-April to create storage space for more highly contaminated water.

The accumulation of radioactive water has been one of the major challenges at the troubled Daiichi plant. More than 100,000 tons of irradiated water is flooding the basements of reactor buildings and adjoining trenches and facilities. Some of the water came from the tsunami, and some from operations to inject water into the damaged reactors to cool them.

Now that the rainy season has started, the level of water is rising, and with it, fears that the it will again overflow into the ocean.

To avoid further large-scale contamination, Tepco is working with French nuclear energy firm Areva S.A. to build a water-treatment facility that can decontaminate 1,200 tons of water per day at the Daiichi plant by around June 15. NISA spokesman Mr. Nishiyama said construction is proceeding on schedule.

But Tepco is bringing in temporary storage tanks with a total capacity of 40,000 tons in June, and 20,000 tons each in July and August, to ensure there is storage space for contaminated water if completion of the treatment facility is delayed.

Separately, Tepco said that power was temporarily lost to the control room serving the No. 1 and No. 2 reactors at Fukushima Daiichi nuclear plant early Wednesday afternoon, but it was restored about three hours later.

The outage blacked out the control room and stopped a data system for some of the radiation monitoring posts. Hydrogen injection into the reactors was also temporarily suspended.

The cooling system wasn't affected, however, allowing workers to continue an operation to cool the reactors.

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