When the glaciers melted and sea levels rose over the following thousands of years, the water table under the Yucatán rose with them.

The cave system filled with water gradually — not all at once, but in a process that unfolded over centuries or millennia as the rising ocean pushed fresh water upward through the limestone.

Hoyo Negro flooded.

Naia’s bones, already on the chamber floor, were inundated.

The chamber that had been air-filled for millions of years became the dark, deep, water-filled space that Nava and his team entered in 2007.

The flooding preserved the bones in a way that surface burial rarely does in tropical environments.