Siri Waterfall, Natural waterfall in Gaua Island, Vanuatu.

Siri Waterfall is a 120-metre-high waterfall on Gaua, a 328.2 km² volcanic island in northern Vanuatu. It lies about 3 km inland from the east coast, where the outflow of Lake Letas, the Mbe Solomul, drops over the escarpment. Below the fall the stream, known as "Big Water", runs another 3 km to the sea.

The name comes from the Nume language and shares linguistic roots with other regional languages, all deriving from an ancient Proto-Torres-Banks word. This linguistic connection reflects the long history of settlement and exchange among the islands in this region.

The name siri means 'waterfall' in the local Nume language, and it is cognate with words for waterfall in neighbouring languages such as Vurës sēriv, Mwotlap na-syip and Mota siriv, all traced to Proto-Torres–Banks *siriβi. The stream below the falls, the Bē Solomul, is known locally as "Big Water".

The waterfall sits about 3 km inland from Gaua's east coast, reached by a forest trail from the coast; the outflow continues 3 km to the sea as the Bē Solomul River, called "Big Water" locally. A flow reading taken in August 2006, in the dry season, was about 5 cubic metres per second, so expect less water in those months. Bring footwear for wet, muddy ground.

The waterfall's name, siri, simply means 'waterfall' in the local Nume language, and it is cognate with words for waterfall in Vurës, Mwotlap, Mota, Dorig, Olrat, Lakon and Mwerlap, all derived from Proto-Torres–Banks *siriβi. The fall was formerly called Santa Maria Waterfall.