On 18 September 2018, an adult individual of Lontra longicaudis was observed stalking and capturing an adult individual of Iguana iguana on the Paranã River, Paranã municipality, Tocantins state, Brazil (12°41’40.16”S; 47°47’11.14”W, 277 m a.s.l.). The area along the river consisted of a dense and preserved riparian forest. The record location is in the Cerrado Biome, in the area of influence of the Peixe Angical hydroelectric power plant (HPP). During the predation event, which lasted about five minutes, I. iguana had just entered the water when it was attacked by L. longicaudis, who captured the lizard with a bite on the neck, dragging it across the river (Fig. 1). With great resistance, I. iguana managed to escape, swimming to the river bank, where it quickly climbed the dirt bank. After that, a L. longicaudis was gone, no longer being observed. No nesting area of I. iguana or food resources were found near the record location, thus the attack could not be attributed to a behaviour of defence or competition between these species. Leia na íntegra.