I recently bought an interesting book called `Jungle Pimpernel` by Lloyd Rhys about the experiences of Jean Victor de Bruijn, a Dutch Captain in Papua New Guinea during World War 2. In it is a fascinating account of canoes that disappeared on a certain lake and what the locals described a a "ghost" but my interpretation is that it was some kind of aquatic cryptid, which was compared by the author to a mermaid. Here is the relevant passage, on pages 51 - 52:
"...but the evil spirit they fear the most is the Mado ,who,like the mermaid,is said to have the habit of luring mortals to a watery grave. The Mado ,or the water ghost,always lives in still water,and has often been said to appear in Lake Paniai, where there are,of course,no currents. Often,somewhere in the woods, you will find still and silent pools,and these are places to be avoided,for there,surely,will be the Mado...one of the long haired creatures will drag you down to the depths of its home..."