Hydrological Activity

Two park rangers pour green dye in to a stream.
Dye tracing allows scientist to follow that path of water from the surface into the cave system below.

NPS Photo

The Link Between Water, Rocks, and Cave Systems

Hydrology is the study of how the Earth’s water flows across and through the land. In karst landscapes like the Mammoth Cave area, much of the water flows underground through caves. Meaning that, for much of the water’s journey, we cannot actually see the water flowing or where it is going.

The lack of being able to see where the water goes can be a big problem. For example, if a tanker truck were to overturn and spill a dangerous chemical in a non-karst area, emergency responders could see where the surface water was moving in that area and would be able to put up protective barriers or “booms” to stop the pollution from spreading to more surface streams. This would keep the dangerous chemical from harming people and the environment through the water system.

However, in a karst landscape, if that same truck were to overturn and spill the same chemical, the chemical could disappear down a sinkhole out of sight and out of reach. The chemical solution (or pollutants) could freely flow through the groundwater and through cave systems underground. Not only could booms not be placed to catch the pollutants, we might not even know where the pollution was going once it left our view.

Following the Path of Water

In order to understand where the water is going in karst landscapes, park managers use specialized techniques to track the water in the park. One of these techniques is dye tracing. In dye tracing, harmless fluorescent dyes are poured into a water source before it disappears into the ground. These dyes are later can be detected at springs and in different areas of the caves. By tracking the dye traces that are performed, maps can be made that show where the water is flowing underground even if we cannot see while we are standing on the surface.

A map showing the watershed around Mammoth Cave National Park. The park is in the center shown in green. It is surrounded by a series of red lines representing streams flowing to the park.
This map shows the results of hundreds of dye traces in the Mammoth Cave region.  It lets us define groundwater basins that drain to different caves and springs in the region.

NPS Graphic

Protecting Our Groundwater

Because area water runs off the surface and goes quickly into sinkholes and into the groundwater, it is extremely prone to pollution by contaminants on the land. These contaminants could include spilled chemicals, animal waste, sewage, or pesticides and fertilizer used on yards and crops. These pollutants threaten cave creatures like endangered Kentucky cave shrimp and ultimately the water and diverse aquatic life of the Green River.

Large amounts of land outside Mammoth Cave National Park feed into the springs and caves that are found within the park. The park works with its partners through the Mammoth Cave Biosphere Region to help in instituting best management practices within the local communities to protect groundwater coming into the park from those areas of contamination.

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11 minutes, 39 seconds

Learn how water connects us all in the Mammoth Cave Biosphere Region. Scientists, farmers, river paddlers, conservationists, and the national park speak about the importance of ground water conservation in a short film created by Lia Nydes of the Center for Environmental Filmmaking in partnership with the Mammoth Cave Biosphere Region, Barren River Area Development District, Western Kentucky University, and the National Park Service.

Learn more about the US Biosphere Network

Workers use heavy machinery to change filters in a large concrete box in the ground.
Underground filters protect cave systems from contamination from water running off parking lots.

NPS Photo

The park is also concerned about pollution that comes from inside the park itself. Parking lots around the hotel and visitor center receive hundreds of thousands of cars on them each year. Some of these cars drip fluids which can pollute the cave system that runs directly below and around the parking lot areas. To protect the cave from this contamination, stormwater from the park parking lots is directed through special filter areas that remove many of the contaminants from the run-off before it can enter the cave.

A sinkhole filled with blue green water.
Karst Topography

Sinkholes, sinking streams, caves and more!

A hiking trail leading into the forest
International Designations

In addition to being a national park, Mammoth Cave is an international biosphere reserve and world heritage site.


Last updated: April 12, 2021

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Contact Info

Mailing Address:

P.O. Box 7
Mammoth Cave, KY 42259-0007


270 758-2180

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