After decades of banning commercial hunting, the population of the endangered giant river otter in South America is no larger than 5000 animals, with slightly increasing populations, and apparent reoccupation of parts of its historical distribution. In Brazil, which may hold the largest populations, the refinement of distributional data and the conduction of censuses in Amazonia were identified as essential for the conservation of the species. To confirm if the species was, in fact, reoccupying its historical area, we present here data collected between October 2004 and September 2008 in Amanã Reserve, Central Amazonia. A total of 18,181 km along 13 water bodies were surveyed in 465 days of fieldwork, resulting in 711 records. Animals presented a uniform occupation pattern, with expansion to new areas, no vacancy of previously used ones, and with frequent reuse of sites along the years. However, considering the number of records/km and sightings/km were almost constant between years, the local population may be experiencing just a slight increase, with animals probably expanding their home ranges. Although our study witnessed some population growth, giant river otters remained at low numbers during the survey, indicating that such population still have not reached its carrying capacity and require continuous attention.