Where do people perform an annual ritual, involving dance and masks made of mud, to honor their river god?

Papua New Guinea people perform an annual ritual, involving dance and masks made of mud, to honor their river god. Bougainville’s bamboo dancing or ‘thhong slapping’ dance, as it is commonly called, is truly unique. Men drum out tenor, soprano and baritone notes to an island tune while women and men sing traditional songs reminiscing about fishing, canoeing, harvesting and feasting.

i believe agnus organum.