A while ago I did a dive in cenote Noc-Ac, north of Merida about half way up to Progresso. Around Merida, the elevation of the Yucatan Peninsula is about 5,000 ft. Since elevation varies by no more than about 1 ft per mile on the peninsula, the elevation could not have been much more or less at Noc-Ac from what it is in Merida.

On the surface of Noc-Ac, as is the case in all cenotes, you find fresh water. While in the cenote, I tasted the water and it was fresh. We penetrated into a cave at the bottom of the cenote and at around 95 ft. I tasted the water again and it was sea water.

Here's my question: If Noc-Ac is thousands of feet above sea level in elevation, how come I found sea water just 95 ft. below the surface?