Xiechi Lake (解池), AKA Yuncheng yanchi (Yuncheng Salt Lake) is the largest natural lake in Shanxi. It's a saline lake used for theproduction of salt.
In summer, intense light and heat cause the algae Dunaliella salina to produce carotenoids as a protection against free radicals. This turns the salt pans brilliant shades of violet, scarlet, magenta, and emerald.