"The High Plains Aquifer, also known as the Ogallala Aquifer, is under stress. Farmers today have to drill ever deeper wells in order to pump water for irrigation, and one recent study found the aquifer to be under more strain than any other in the United States."
Facts about the depletion of the Ogallala Aquifer:The industrial-level pumping of water from the aquifer began after World War II.
By 1980, the aquifer's water levels had dropped by at least ten feet in most of the regions that took advantage of it.
Some regions of the High Plains, at that same time, had seen a 100-foot drop in their water level.
These days, the water being pulled out of the aquifer annually is equal to eighteen Colorado Rivers.
The northern end of the Ogallala Aquifer is less affected by the overuse. The southern end is the part of the aquifer that is less likely to recover, as it doesn't receive as much precipitation annually.
Shown below is a map of the Ogallala Aquifer, how long it has been irrigated in different regions, and a link to the full article.