A census of crocodilians was made in a lake permanently linked to the Rio Trombetas, within a Biological Reserve of the IBDF, as well as at the mouth of the River, outside the Reserve. Estimates of size and data on the localization of the animals in the environment were undertaken. Only Caiman crocodilus crocodilus was identified, in a total sample of 33 individuais, most below 1 m in total length. Even then, there were reproductive individuals in both samples.