"Blood falls" in Antarctica. This water contains ferrous iron, which, combining with atmospheric air, oxidizes and forms rust. It gives the waterfall that blood-red colour

Source:

/r/interestingasfuck /u/XyRow666

I honestly found this one googling around, but XyRow666 presented a far nicer collage than anywhere else I could find.

more info: https://www.atlasobscura.com/places/blood-falls

Roughly two million years ago, the Taylor Glacier sealed beneath it a small body of water which contained an ancient community of microbes. Trapped below a thick layer of ice, they have remained there ever since, isolated inside a natural time capsule. Evolving independently of the rest of the living world, these microbes exist in a place with no light or free oxygen and little heat, and are essentially the definition of “primordial ooze.” The trapped lake has very high salinity and is rich in iron, which gives the waterfall its red color. A fissure in the glacier allows the subglacial lake to flow out, forming the falls without contaminating the ecosystem within.