The Ogallala Aquifer is a vast, subterranean reservoir that has sustained life and agriculture across the American Great Plains for decades. This natural resource underlies a large swath of the central United States and is often called the lifeblood of American agriculture. Its presence enables the immense productivity of the region, transforming semi-arid grasslands into one of the world’s most productive agricultural zones. The aquifer is immense in volume, yet finite in its ability to recharge, creating a complex water management challenge that defines the region’s future.
Defining the Ogallala Aquifer
The Ogallala Aquifer is the largest component of the High Plains Aquifer System, stretching over approximately 174,000 square miles beneath eight states. This formation includes parts of South Dakota, Wyoming, Nebraska, Colorado, Kansas, Oklahoma, New Mexico, and Texas. The aquifer is not an underground lake, but a layer of saturated sand, silt, clay, and gravel that stores water within its pore spaces.
The formation was created millions of years ago from sediment washed down from the Rocky Mountains. Much of the water is considered “fossil water,” meaning it was deposited during the last Ice Age. This water is not replenished at a rate that can match modern human usage. The depth and thickness of the saturated material vary dramatically, with the thickest part lying beneath Nebraska.
The Measured Volume
The U.S. Geological Survey (USGS) provides the most comprehensive estimates of the water contained within the Ogallala Aquifer. In 2015, the total recoverable water in storage was estimated to be about 2.91 billion acre-feet. This volume is enough water to cover the entire continental United States with roughly 1.5 feet of water.
Not all of this water is practically accessible or “economically recoverable.” The recoverable volume is calculated using the concept of specific yield, which is the amount of water that will drain out of the material under gravity. If the water table drops too low, the remaining water is too deep or the saturated material is too thin to be profitably extracted.
The USGS uses a network of thousands of wells across the eight states to measure water levels and changes in saturated thickness. Scientists estimate water loss by comparing current levels with predevelopment water levels, which existed before large-scale pumping began around 1950. Since predevelopment, the aquifer’s total recoverable water has declined by approximately 9%, or about 273.2 million acre-feet.
Water Usage and Economic Reliance
The water in the Ogallala Aquifer has enabled a flourishing agricultural economy across the Great Plains. The region overlying the aquifer contributes significantly to the national food supply, producing about a quarter of U.S. crops and livestock. This output is highly dependent on irrigation from the aquifer, especially given the semi-arid climate.
Approximately 95% of the water pumped is used for irrigated agriculture and livestock production. The aquifer accounts for about 30% of all groundwater used for irrigation in the United States. Crops such as corn, wheat, and cotton, along with large-scale cattle production, rely heavily on this source. While the aquifer also serves as the primary water source for municipal and industrial uses, crop irrigation is the overwhelming driver of demand.
Depletion Rates and Future Projections
The primary challenge facing the Ogallala Aquifer is the imbalance between water extraction and natural replenishment. Since the majority of the water is ancient “fossil water,” the natural recharge rate is extremely slow. It often averages less than one inch per year across much of the area, and in arid parts like Texas and New Mexico, recharge can be as low as 0.024 inches annually.
This slow recharge rate is overwhelmed by the high rate of pumping for irrigation, which accelerated after World War II with the advent of center pivot irrigation. Since 1950, water levels in the aquifer have dropped by an average of 15.8 feet. Declines are significantly worse in the southern portions; for instance, parts of the Texas Panhandle have seen drops of 44 feet, and Kansas areas average over 28 feet.
Based on current trends, the usable lifespan for some heavily pumped portions of the aquifer is measured in decades. Northern regions, particularly in Nebraska, have seen relatively stable or rising water levels. However, the southern and central sections face a future where the resource may no longer support current irrigated agriculture. Models project that continued depletion will force transitions to dryland farming, fundamentally altering the economy and landscape of the Great Plains.