The American crocodile, Crocodylus acutus, has experienced important population declines worldwide due to human persecution, overexploitation and habitat loss. C. acutus remains critically endangered in some countries such as Colombia where the lack of detailed surveys on its ecology and distribution constitutes a major barrier to the development of effective conservation strategies. We conducted a three-year capture-recapture study to investigate the demographic status of C. acutus and to identify environmental variables likely to in uence its distribution in Portete Bay (Colombia). We estimated the crocodile population to be relatively small (< 140 animals), to include very few adults, and to demonstrate a very strong de cit in females in the juvenile class. Both mean air temperature and relative humidity were positively correlated with the number of sightings. In contrast, mean water salinity was found to decrease the probability of observing a crocodile, presumably due to juvenile preference for low salinity areas. Our findings suggest that the population of C. acutus in Portete Bay is at risk and may require human intervention to assure its persistence.