Every year, visitors of Peru’s Vilcanota mountain range are treated to a unique natural phenomenon, a river running blood red through the pristine rocky valleys of Cusco.

Located approximately 100 kilometers from the city of Cusco, near the well-known Palcoyo Rainbow Mountain, the red river is known as Palquella Pucamayu by the locals. It only runs red for about 5 kilometers before mixing with other streams and small rivers in the area, at which point the color becomes diluted, losing its unique hue. The best time to see the red river in person is during the rainy season (December – April), because the color of the water is directly influenced by the level of precipitation. For most of the year, Palquella Pucamayu is a muddy-brown color, but during the rainy season, large quantities of soil rich in iron oxide are carried down from mountains and color the water bright red.

Photos and videos of the red river of Cusco have been doing the rounds online for years, and even though it is a well-documented phenomenon, many still doubt that the river exists. While software like Photoshop and other more powerful AI-powered editing apps can be used to create such an otherworldly-looking illusion, this particular one is genuine.

The rainy season is not the best time to trek through the Vilcanota mountain range, but if you want to witness the blood-red waters of Palquella Pucamayu in person, there is no better time.

For more fascinating bodies of water around the world, check out the world’s narrowest river, and the most radioactive river in the world.