Mercury, krypton, nickel, and iron with anomalous isotopic compositions were found to be produced on or in gold electrons during light water electrolysis. In addition, silicon and magnesium with anomalous isotopic compositions were also detected in the precipitates separated from the gold electrode electrolyzed at extremely high current densities. After the electrolysis, the surface of the electrode exhibited an extraordinary structure, i.e., a number of microcraters like volcanoes were developed. The structure of the outside wall of the craters was very much like that of the precipitates, and hexagonal crystallite layers in the inside wall of the craters suggested a partial recrystallization of the electrode material due to some intense heat evolution. The craters developed along the rim of the microcracks, microholes, and scraped edges of the electrode. These results suggest that some nuclear transmutation reactions occur during the electrolysis to produce these effects.