Why is the stream at this Kentucky national park green? It’s not for St. Patrick’s Day

Streams at Kentucky’s Mammoth Cave National Park may look festive for St. Patrick Day’s, but the holiday is not the reason for the bright green color.

Officials at the national park used the St. Patrick’s Day holiday to explain why green dye had been filtered into their waters. It’s a process called dye tracing, which is used to study groundwater movement.

“Dye traces are necessary to map out the hydrology of Mammoth Cave, to locate conduits inaccessible to cave surveyors, and help us to understand the complex networks of flow paths through the aquifer,” Mammoth Cave wrote on Facebook.

But don’t worry, the fluorescent dye used in the task is nontoxic, according to US-Parks.com.

The process helps solve problems “involving the origin, destination, routing and velocity of groundwater flow,” according to DyeTracing.com from Western Kentucky University’s Crawford Hydrology Laboratory.

Dye trace studies are important because they allow researchers to determine where pollutants come from, the National Parks Service said.

“A key reason why the Mammoth Cave System is the world’s longest known cave is that its passages extend over several major ground-water basins,” Mammoth Cave said. “Precise location of these water basins is critical for understanding and protecting the cave and its remarkable aquatic ecosystem!”

This story was originally published March 17, 2021 at 9:26 AM with the headline "Why is the stream at this Kentucky national park green? It’s not for St. Patrick’s Day."