One of Japan's opportunities to tap cleaner, cheaper energy and reduce its dependence on imported oil has run into a problem: millions of naked bathers.

The dispute is over volcanically heated water deep underground that geothermal power plants would tap to generate electricity. Japan, with nearly a tenth of the world's active volcanoes, also has thousands of hot spring resorts whose owners oppose plans to siphon off steaming mineral waters.

"Developers say geothermal plants don't affect hot springs, but if something goes wrong, it's our responsibility to prove cause and effect," said Toyoshiro Kawazu, managing director of Hizenya Hotel Group, whose family owns a 300-year-old spa in Kyushu.