A small body of water in Hawaii has turned such a bright pink it could have been used as a set for the movie Barbie.
But the unusual color-changing event has some experts concerned.
Scientists say extreme dry weather, or drought, may be the reason for the color.
For now, they are warning people not to enter the body of water, called a pond, and not drink from it.
Workers at the Kealia Pond National Wildlife Refuge on the island of Maui have been watching the pink water since October 30.
"I just got a report from somebody that was walking on the beach, and they called me up like, 'There's something weird going on over here,'" said Bret Wolfe, who leads the refuge.
Wolfe was concerned the bright pink could be a sign of an event called an algae bloom.
An algae bloom happens when simple plants called algae grow out of control and cause harmful effects on humans and animals.
But lab tests found harmful algae was not causing the color.
So investigators started looking at an organism called halobacteria as a possible cause.
Halobacteria are a kind of single-celled organism that do well in bodies of water with high levels of salt.
The amount of salt inside the Kealia Pond area is currently greater than 70 parts per thousand, which is twice the amount of salt in seawater.
Wolfe said the lab will need to perform DNA research in an effort to identify the organism.
Researchers feel that Maui's drought is likely adding to the situation.
Normally, another body of water called Waikapu Stream feeds into the pond and raises water levels there.
But Wolfe said that has not happened in a long time.
When it rains, water flows from Waikapu Stream into the pond and then into the wider area that is now pink.
This reduces the amount of salt and could possibly change the water's color.
"That might be what makes it go away," Wolfe said.
None of the workers, or even some volunteers who have been around for 70 years, have seen the pond this color before.
It has been through periods of drought and has had high amounts of salt before.
But Wolfe is not sure why the color has changed now.
Visitors have come to the area after photos of the pink pond appeared on social media.
Wolfe said he would love to have visitors come to learn about local aims to protect nature.
He joked, "But no, they're here to see the pink water."
He understands everyone's interest.
"If that's what gets them there, it's OK," he said.
The wildlife area is a wetland that protects endangered birds like the Hawaiian stilt and the Hawaiian coot.
It also protects birds that are traveling to warmer areas in the winter.
The water does not appear to be harming the birds, Wolfe said.
As a protected area, people are not supposed to enter the pond or let their animals in the water.
But officials have issued a special warning for people not to enter the water or eat any fish caught there.
I'm Gregory Stachel.