This past October, a saltwater marsh at the Keālia Pond National Wildlife Refuge on Maui, Hawaii, turned a shocking shade of pink. To find out what caused the color change, the refuge sent water samples to the University of Hawaii and George Washington University for testing. The results suggested that the marsh contained an abundance of single-celled microbes called purple sulfur bacteria, which naturally have a rosy hue.

Bret Wolfe, the manager of the refuge, says scientists aren’t sure why this bloom was so intense and vibrant. He says it could be because the area was experiencing a drought—a prolonged dry period. As water evaporates—or changes from liquid to gas—the water levels in the marsh fall. This likely increased the concentration of bacteria enough to turn the marsh bubble gum pink. The rainy season, which lasts from November to March, put an end to this colorful phenomenon.