With the help of mathematics, the original color of Yellowstone National Park’s Morning Glory Pool may have been discovered. According to recent research, the yellow, green and blue sight at the Yellowstone National Park may have not always been so colorful.

Named by the blue trumpet-shaped flower, the Morning Glory Pool used to be clear and colored like a robin’s egg blue. But today, the colors shown are orange on the outer edge, which fades to yellow then green in the deepest part. Park researchers have blamed the changing colors on garbage being thrown into the pool by tourists.

Morning Glory Pool

“By the 1950s, people had thrown so much trash, rocks, logs and coins into the spring that Morning Glory Pool became known informally as the ‘garbage can,'” according to the Park Service. The garbage has also reduced the flow of hot water into the pool and lowered the temperature to around 50 degrees. The bacterium that has since bloomed in the pool is what is causing the vivid array of colors we now see.

When researchers Joseph Shaw and Michael Vollmer initially began looking at the pool, they realized there was no mathematical model to figure out how different variables were affecting the pool’s color. When Shaw and Vollmer considered the depth of the pool, they were also able to determine that the water absorbed different colors—like oranges and reds—as it got deeper. Different communities of microbes have lended to different colors in the pool.

“The pool center — though presumably covered by the yellow mat — appears deep blue, indicating that the pool is deep enough that backward-scattered sunlight from the water is the dominant component of upwelling light,” wrote the study’s lead author, Paul Nugent, and his colleagues. Paul Nugent is a computer engineering researcher at Montana State University; Joseph Shaw is an optical science professor at Montana State University; and Michael Vollmer is a professor of experimental physics at Brandenburg University of Applied Sciences in Germany.

With the same model, the three researchers were also able to analyze some of the park’s other famous magma-heated pools to determine what they might have looked like before civilization came along.