Réunion giant eel
According to a letter in the magazine known as The Field, written by Courtenay Bennett, gigantic eels are living in the deep pools of Réunion, a large island just west of Mauritius. In the article, Bennett wrote that when he was consul at Réunion in the 1890s, he saw a dead specimen of some kind of eel that was fished out of Mare à Poule d'Eaux. Bennett didn’t know the species but said it was as thick as a man’s thigh. He didn’t specify the length, but based on its width, it probably would have been 15 to 20 feet long.
This would make the eels Bennett witnessed to be significantly larger than the Giant mottled eel (Anguilla marmorata), the largest known freshwater eel in Réunion, with unusually large specimens reaching five feet. According to the article, during heavy rains in the winter, these giant eels could be seen circling the edge of the pools, which Bennett interpreted as the eels trying to search for a way out. When they are doing this circling behaviour, they are easy targets for hunters, who catch them using a harpoon and a rope secured onto a tree. The giant eels would then be sold as meat. Since there have been no subsequent sightings, perhaps they were hunted to extinction, or simply never existed.