The picture above is of a real lake. The picture hasn’t been Photoshopped. The lake isn’t filled with Pepto-Bismol, bubble gum, or pink food dye. It’s just naturally pink.
Australia's Lake Hillier is situated on an island in the Recherche Archipelago, a collection of islands to the south of Western Australia. The lake is about 2,000 feet (600 meters) long and 800 feet (250 meters) wide but, because it’s not on the mainland, it went undiscovered until 1802. That year, a British explorer summited a mountain and eyed what he called a "small lake of rose colour," Jeopardy! champ Ken Jennings wrote in Conde Nast Traveler. So, as far as we know, it’s always been pink.
The pink color isn’t an optical illusion, either. If you go to the shores of Lake Hillier, you’ll see that the pink hue remains, although it’s muted a bit, as seen below. And if you scoop some of the water into a pail or jar (ideally a clear one), the water still remains pink.
So what causes this phenomenon? While there are a few plausible explanations as to why Lake Hillier is pink, the most common theories center on salt and algae. Lake Hillier has a very high concentration of salt, comparable to the Dead Sea, which has near a 33% salinity (making it nearly 10 times as salty as the oceans). Second, Lake Hillier is home to a type of algae known as Dunaliella salina. Unlike most algae, which turns bodies of water into a murky green color, Dunaliella salina has a reddish pigment which helps it absorbs light. Because this algae thrives in salty environments—and very few other life forms can—its overwhelming quantity might be the reason Lake Hillier is a deep, thick pink.
And while you probably don’t want to drink the water, it’s safe for humans to swim in it. (The lake is hard to get to, though—you need to take a helicopter from the mainland to the island). But don’t expect to practice your breaststroke or crawl—you won’t find it very easy to navigate through the waters. The high salinity of the lake means that you’ll bob along, floating the whole way like "a cork in a bottle of pink, pink wine," as Jennings puts it.