Scientists have finally solved the century-old mystery of the “Blood Falls” in Antarctica. According to a new study published in the Journal of Glaciology, the flowing water gets its red colour from iron-rich brine, which oxidises as it comes in contact with air – the same way iron rusts.

Blood Falls is located in Antarctica’s McMurdo Dry Valleys and pours out of the Taylor Glacier. First discovered in 1911, experts had earlier assumed that algae in the water gave it the strange red colour.

Researchers used a type of imaging below the glacier to help their study. They found a complex network of brine-rich subglacial rivers and a subglacial lake. Besides the blood-red colour, the salt content in the water also prevents it from freezing in Antarctica’s sub-zero temperatures.