We studied distribution, habitat selection, and reproductive ecology of the Magdalena river turtle, Podocnemis lewyana, from January to June 2003 and from January to March 2005 in the mid and low Sinú River, Córdoba, Colombia. The southern limit of its distribution occurs in the town of Carrizola, and the northern limit is near La Doctrina. We found more turtles of bigger size classes in the mid basin than in the low basin. Ninety-two individuals were observed basking in the river. Larger turtles were mostly observed in deep pools (> 3 m) with loamy or sandy bottoms, with easy access to basking sites, such as riverbanks, fallen trees, or beaches, and in areas with all types of shoreline vegetation but especially with riparian forest. Smaller turtles were found in colder, shallower, and more turbid waters than were adults, mainly in areas without riparian forest or in pastures with few trees, usually hidden in pastures flooded by the river. Adults ventured farther from shore than did juveniles. Along the study area, 5 nesting beaches were located: 3 in the mid basin and 2 in the low basin. Main nesting sites were sand and gravel beaches, but riverbanks were also used. Nesting occurred in small groups or individually in 2 reproductive seasons: one from December to March and the second from June to August. The main threats identified for P. lewyana in the Sinú River were floods caused by water release by Urrá Dam, human consumption and exploitation, nest damage caused by beach mining, and riparian forest destruction for pasture establishment.