From our vantage point high over the Indian Ocean, we can see the "underwater waterfall" that exists just off the Le Morne Brabant peninsula on the Mauritius coast . This is really an optical illusion created by the trails of silt and sand deposits on the seafloor as they are carried by sea currents over the edge of an ocean shelf — it's not really a genuine waterfall. Though at first sight it does appear like the ocean is falling into a huge, mysterious, marine sinkhole.