According to Dante, the Styx is not just a river but a vast, deathly swamp filling the entire fifth circle of hell.

It sounds a lot like Lake Natron in northern Tanzania, where temperatures can reach 60 °C and its alkalinity is between pH 9 and pH 10.5. When salt islands form in the lake, lesser flamingos take the opportunity to nest – but it is a risky business, as this calcified bird illustrates...
Credit: Nick Brandt. Link: New Scientist

Deadly lake turns animals into statues by Rowan Hooper, New Scientist