YUZAWA CITY, JAPAN — Tarobee Ito, 69, is the guardian of a family legacy that has survived for more than 12 generations, since the middle of the Edo period: He manages Tarobee Ryokan, a traditional Japanese onsen ryokan, or hot spring inn, named after an 18th-century ancestor who established it as one of about a dozen inns at the Oyasu thermal gorge near Yuzawa City in Akita Prefecture, northern Japan.

But Mr. Ito’s heritage may be under threat. The white steam, rising lazily from the thermal springs, has attracted developers with plans for a geothermal power plant in the Kurikoma Kokutei Koen, a mountainous area behind his inn that is a national monument.

Mr. Ito professes to be not overly worried. “The developers have promised to stop the process if they see a change in hot spring flow at any point,” he said.

But pressures to develop the thermal energy potential of the region are strong. Japan has been struggling to find alternative energy resources since March last year, when a tsunami created by an earthquake destroyed the Fukushima Daiichi nuclear power plant. Because of safety worries, the country’s 54 nuclear reactors were shut down after the disaster and only two have since resumed operations.