Le Morne Brabant on the southwest coast of Mauritius has a cool optical illusion offshore: water flowing between two reefs pulls sand out to sea, giving the appearance of an underwater waterfall.
YouTuber RubenMRU says:
So the day after my birthday this year saw one of my dreams come true... Vassen Kauppaymuthoo of Delphinium Ltd took me out on a boat trip to the south west coast of Mauritius and we've captured the now famous Underwater waterfall of Mauritius... Now it's not really a waterfall, it only appears to be one from above - this illusion is caused by the trails of sand on the sea floor, being dragged away by water going between the opening in the reefs
Earthporn has some other lovely images:
Some good ones on Instagram, too: