An underwater waterfall?

From this vantage point high over the Indian Ocean, we have a spectacular view of the 'underwater waterfall' off the coast of Mauritius. Actually, this is an optical illusion. We're looking at the trails of sand and silt deposits on the seabed being washed by ocean currents through an opening between coral reefs. But at first glance, it looks like the ocean is pouring into some massive unseen hole.
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