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A worker walks through the underground Furukawa reservoir under construction in Tokyo, Japan, on Thursday, Aug. 7, 2014. The underground regulating reservoir tunnel is 3.3km long and its bore is 7.5m. When it's completed in 2016, the 3.3-kilometer (2-mile) reservoir will be able to handle 135,000 cubic meters of water, enough to fill 54 Olympic-sized swimming pools. Photographer: Noriyuki Aida/Bloomberg via Getty Images

A worker walks through the underground Furukawa reservoir under construction in Tokyo, Japan, on Thursday, Aug. 7, 2014. The underground regulating reservoir tunnel is 3.3km long and its bore is 7.5m. When it's completed in 2016, the 3.3-kilometer (2-mile) reservoir will be able to handle 135,000 cubic meters of water, enough to fill 54 Olympic-sized swimming pools. Photographer: Noriyuki Aida/Bloomberg via Getty Images