MEXICO CITY, MEXICO — Mexico City is a massive expanse of a city, and it's infamous for being the most populous metropolis in North America.

This massive city is sinking fast under its own weight, and has already sunk too low to be saved. Here are the details:

A new study, published in the journal JGR Solid Earth, reports that Mexico City is sinking at an unstoppable rate, with some parts sinking up to 50 centimeters per year over the past few decades.

The massive city was built on a dry lake bed that contains water aquifers which have held up the city in the past.

But centuries of pumping water from these aquifers have made them so empty that the surrounding clay sheets are cracking and compressing.

If the rate of sinking continues, it would lead to the contamination of drinking water for the city's 21 million people.

More than three-quarters of the city's drinking water comes from wells that extract water from the ground and continue to deplete its aquifers.

Experts first noticed the sinking in 1900, when subsidence was recorded to be about 9 centimeters a year.

Drilling for groundwater wasn't capped until the late 1950s, by which time the city was sinking at a rate of 28 centimeters a year.

This cap initially slowed the rate of subsidence, but the sinking accelerated again as the city's population and buildings increased exponentially.

Geotechnical engineer Eddie Bromhead from Kingston University in London told The Guardian: "If you put heavy buildings on that kind of ground, and use shallow foundations, the soil compacts. So that, along with removing the water, is why Mexico City is such a mess."