Sentani Lake is a 104 square kilometre, 171-foot deep lake in the Jayapura Regency in the Papua Province, located 36 kilometres inland. Lake Sentani is well known for its remote location and many species unique to the lake, like the Sentani rainbowfish, Sentani gudgeon and Sentani goby.
One species that is believed to inhabit the lake that is not scientifically known, however, are sharks. These sharks have been mentioned by locals in their ethnozoology. The first detailed report was during WWII when American anthropologist Dr. George Agogino reported his encounter when he was stationed at Lake Sentani against the Japanese army. While there, he and his army unit needed food, so he dropped a grenade into the lake to blast fish out of the water. Surprisingly, a fairly large shark floated upwards to the surface. He measured it to be 12 feet long and sketched the animal before it sank again. Agogino’s sketch was not detailed enough to identify the species but seemed unremarkable: save the fact that it was in a lake.
Although sharks are commonly thought to be exclusively saltwater, the bull shark can survive brackish water. Bull sharks have been observed inhabiting the Tigris, Euphrates, Ganges, Mississippi, and Lake Jamoer, a lake in New Guinea that’s quite close to Lake Sentani. The only problem with this theory is no large rivers connect Lake Sentani to the ocean, but there is another possibility for how sharks may have arrived at the lake.
In early 2019, a devastating flash flood occurred in northwestern New Guinea. Shortly after, multiple blacktip reef shark pups were found dead Lake Sentani, unable to survive in freshwater. Presumably, the sightings of sharks in Lake Sentani are the ancestors of bull shark survivors from similar flash foods that managed to live in the lake and possibly even have a breeding population.