Underwater Waterfall (Illusion) is a waterfall located in the south-west of Mauritius, one of a number of spectacular cascades found in the volcanic interior and coastal margins of Mauritius.

Mauritius was formed by volcanic activity approximately 8–10 million years ago, and the island's rivers and streams cut through basalt formations to create waterfalls in the central plateau, Black River district, and coastal hills. The wet season (December–April) produces the most dramatic flows; some falls reduce to trickles in the dry months of July–September.

The underwater waterfall illusion near Le Morne is a mesmerizing optical effect created by sand and silt deposits. Best viewed from above, it’s one of Mauritius’ most photographed natural phenomena.

Getting to most waterfalls requires a walk, ranging from a brief 10-minute stroll to a 2–3 hour hike. Sturdy footwear is recommended — volcanic rock can be slippery, and paths become muddy after rain. Some falls are within private nature reserves or domaines that charge an entrance fee.

Swimming at the base of waterfalls is possible at some sites. Check conditions before entering — currents can be stronger than they appear after heavy rain. The water is typically fresh and clear. Natural pools carved in basalt are a highlight of several sites.

The best time to visit waterfalls in Mauritius is during or just after the wet season (January–April) when flow is strongest, though the access trails can be muddy. The dry season offers easier walking but reduced flow.