Navy personnel attempted to rescue both victims, but the woman, 65, died at the scene. Her 70-year-old walking partner is still in serious condition at a hospital.
Though the victims' names have not been released, authorities said the woman had a driver's license from Wisconsin, while the man's was from Nebraska.
According to the Examiner, 51 Americans have drowned in Mexico in the last two years.
Notable deaths of 2014 [PHOTOS]