There is a water current that rung along the west coast of South America from Chile up past Ecuador called the Humboldt Current. The reason why the water in Mancora or Trujillo are freezing.
These waters come from the Antarctica at the South Pole in the South Pacific. Every few years the water is actually a little warmer and it is called the El Niño, the El Niño is not unusual, it happens ever 3-7 years and caused headaches for the locals.
The bottom line is if you wish to lay around in the waters as you could in some bay in Southeast Asia and bask in the sun, it is not going to happen, the waters are not comfortable, and however for sure they will cool you off very good.