Prince Piero Ginori Conti tested the first geothermal power generator on 4 July 1904, at the Larderello dry steam field in Italy. It was a small generator that lit four light bulbs. In 1911, the world's first geothermal power plant was built in the Valle del Diavolo ("Devil's Valley"), named for the boiling water that rises there. It was the world's only industrial producer of geothermal electricity until 1958, when New Zealand built a plant of its own in Wairakei. In recent years concerns have been expressed about the sustainability of its steam supply, as a 30% drop in steam pressure levels has been recorded from the maximum levels of the 1950s.