Previous studies, based on limited data, found elevated levels of mercury in carp in Lake Chapala, Mexico. The extent of mercury contamination in carp throughout the Lake has not been determined. In order to obtain reliable information about total mercury concentration in carp (Cyprinus carpio), 262 fish from 27 sites (approximately 10 fish per site) throughout the lake were analyzed. Results were expressed as the mean and median of the results at each site. Only one of the samples exceeded Mexican National Standard (1.0 ppm) for mercury in fish flesh. We discuss these results in comparison to World Health Organization (WHO), US Food and Drug Administration (FDA) and US Environmental Protection Agency (US EPA) criteria; many of our samples exceed these criteria based on Tolerable Daily Intake (TDI) or Reference Dose (RfD). ANOVA of four groups of mercury results clustered by distance from the Lerma showed statistically significant differences (P = 0.0071) between the group closest to, versus farthest from, the Lerma River.