Across southern Idaho, an incredible hydrologic feature is shifting, filtering, trickling below the feet of Idahoans every day: the Eastern Snake River Plain Aquifer (ESPA). This aquifer is responsible for some of Idaho’s most remarkable attributes, from natural wonders like Thousand Springs to Idaho’s abundant crop output.
Aquifers are made up of water-saturated bedrock, a great, slow-moving river of water captured in stone. Think of a giant, rock sponge! Aquifers not only provide both groundwater storage, but filtration. The saturated yet porous rock traps sediment and other particles (like bacteria) as water flows through, providing natural purification.
Aquifers can offer a plentiful source of clean, cold water for drinking water and irrigation water. The Eastern Snake River Plain Aquifer, in particular, is a key water resource of Idaho’s. Want to get to know this truly-hidden Idaho gem a little better? Here’s 10 fast facts about the ESPA.
- The ESPA covers an area of approximately 10,800 square miles. Stretching from St. Anthony to King Hill and spreading crosswise from Craters of the Moon National Monument to Pocatello, the overall square mileage of the aquifer is nearly 1,500 square miles larger than the state of New Hampshire.
- The ESPA is estimated to hold between 200 to 300 million acre-feet of water, which is the same amount of water held behind the shores of the fourth-largest Great Lake, Lake Erie.
- We have plate tectonics to thank for the ESPA. As the North American tectonic plate moved southwest over the static Yellowstone hotspot, the volcanic plume heated and melted the crust of the earth, leaving a trail of porous rhyolite and basalt rock in its wake. It’s this porous, easily-saturated rock that holds and filters water so well!
- Hagerman’s spectacular “Thousand Springs,” is thanks to the ESPA. The crystal-clear spring waters that erupt from the canyon walls of the Mid-Snake River are the discharge points of the aquifer, where the groundwater reunites with the Snake River.
- Water flowing from those very springs today could have been in the aquifer longer than Idaho has been a state! It can take a drop of water starting near Yellowstone 150-200 years to move through the entire aquifer.
- The ESPA provides drinking water to approximately 300,000 Idahoans—that’s 15.7% of Idaho’s population!
- The aquifer not only sustains thirsty people, but thirsty crops too: the ESPA provides over half the water used by Eastern and South-Central Idaho’s farmlands.
- While the crisp, cool temperature of groundwater from the aquifer may of snow fields in Montana and the cold headwaters of the Snake River in Wyoming, approximately 60% of the aquifer’s “recharge”—water entering and refilling the aquifer—is made up of re-absorbed irrigation water.
- The ESPA, while vast and impressive, is threatened by climate change. In recent years, the water level of the aquifer has fallen dramatically with a corresponding rise in temperatures and a decrease in annual precipitation.
- The ESPA, despite being excellent at filtering, cannot stop all pollutants; the groundwater has absorbed an alarming amount of nitrogen from the overapplication of agricultural fertilizers, animal manure, and other sources in amounts that far exceed what typical crops can uptake. As the aquifer’s waters deplete, the concentration of nitrogen will grow; this is especially concerning as it can take 40-50 years for nitrogen to dissipate from the groundwater supply.
Dense mats of aquatic weeds (known as macrophytes) are an indication of too much phosphorous and other pollutants in the Snake River. Extensive weed beds will be killed by the pesticide application.
The Eastern Snake River Plain Aquifer is an incredible but threatened resource. The good news is that there are many ongoing efforts to address the problem. The Idaho Conservation League is engaged in a multi-year campaign to restore the Snake River in southern Idaho to a swimmable and fishable condition, with a key objective of this campaign focused on the protection and restoration of groundwater quality.
However, we won’t be able to protect this resource alone. This September is ICL’s annual membership drive; we hope you’ll join us as a member, and help us to continue advocating for sustainable farming practices and creating a cleaner, more resilient aquifer. Become a member today!