In the Cabo Rojo National Wildlife Refuge in southwestern Puerto Rico, a quick walk through a mangrove swamp leads to an unexpected sight: cotton-candy pink water glistening in the sun. This is Las Salinas, the pink salt flats—a 1,249-acre area of two 18-inch-deep natural lagoons that have been altered to mine salt, and an Instagram-worthy destination for the fluctuating pastel shades of the water.
The color ranges from reddish brown to bright pink to cloudy white, all depending on the day and the weather, though more often than not it’s pink. The hue is thanks to a combination of algae, bacteria, salt and water.
An algae called Dunaliella salina is mainly responsible for the water color in the salt flats. Even though it’s in the green algae family, it’s stuffed full of carotenoids—the pigment that gives many orange and red fruits and vegetables their color. In this particular algae, those carotenoids are red. Archaea, a bacteria and prokaryotic organism (meaning it’s a single cell and doesn’t have a nucleus), floats around in the salt flats as well. It has a pigment called rhodopsin that also appears red.
The color of the water depends on the amount of algae and bacteria in the ponds, explains Lilliam Casillas Martinez, a biologist at the University of Puerto Rico at Humacao who has co-authored several studies on the microorganisms contained in the salt flats. “We have rainy seasons, when the salinity levels decrease [because there’s more water in the ponds]. When there's less salt, the Dunaliella survives and the ponds look brownish-red,” she says. “During the dry season, it gets really salty. The Dunaliella dies and the archaea and bacteria take over. Then it becomes pink, pink, pink.”
Other hyper-salinated spots around the world have a pinkish hue too, like the pink Lake Tyrrell in Australia, the salt ponds in San Francisco Bay, and the Santa Pola saltern in Spain (though this one is more red and brown than pink). But Cabo Rojo has spectacular biodiversity and is incredibly easy to get to—making it great for a quick day trip while visiting the island.
Salt is mined from the flats regularly—in fact, it’s one of the oldest businesses in Puerto Rico, Casillas Martinez says. When Christopher Columbus landed on the island in 1493, the Indigenous Araucos and Taíno were already extracting salt from the flats and had been since about 700 C.E. After the Spanish arrived, they began to export the salt and enslaved the Indigenous populations to do the hard labor of raking up the salt and cleaning it. But locals didn’t approve, so they fought the Spanish for control.
“There is a beach close to the salterns [man-made pools where seawater evaporates] that is called Combate, which means ‘fight,’” says Casillas Martinez, where the locals battled the Spanish for the salt flats. The salterns are walking distance from the beach, heading right along the coast. Or, you can drive through the wildlife refuge from the beach to get there.
Las Salinas and the Cabo Rojo National Wildlife Refuge came under the purview of the U.S. Fish and Wildlife Service in 1974, though a private company still mines salt there, now using heavy equipment to do the hard work.
The rainy season, April through November, makes for the best time to visit the salt flats, according to Casillas Martinez. While the watery salterns are a reddish-brown, animal life (including a huge population of sea monkeys) flourishes at this time and the surrounding plant life is newly green. But the salt flats are their pinkest in the dry season, from December to March. With less rain to dilute the organisms causing the color, visitors can see dried salt crystals lining bright pink salt flats. About 40,000 migratory birds, including brown pelicans, snowy plovers and great blue herons, winter in the salterns.
The Cabo Rojo Salt Flats Interpretive Center is the starting point for guided tours (contact the staff in advance for reservations), as well as self-guided walks. From there, visitors can watch a video about all the bird species in the flats, read about the area’s ecology and geology, and head out to climb the adjacent three-story-tall observation tower and then take a hike through the flats, walking both around the perimeter and through the middle of the saltern pools themselves on concrete dividers. Taking salt, wading into the pools, or climbing onto salt mounds is prohibited.
“You have mountains of salt,” says Casillas Martinez. “If you go there, it's funny because you think it's snow. But it's not snow. And during the afternoons in the rainy season, it's full of migratory birds. It's wonderful to be there in the afternoons. You see all these birds, drinking and singing, and it's beautiful.”