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.
NBC reportedly holds celebs hostage to Jimmy Fallon's show
Millions of Getty images now available for free via embed tool