A decreased tannin load during 2006–2007 in a northern Florida blackwater river allowed us to make observations on the ecology of the Suwannee cooter (Pseudemys concinna suwanniensis), a species otherwise usually studied in clear, spring-fed rivers. We conducted a capture–mark–recapture study of this protected species and recorded the locations of marked individuals throughout a > 7.4-km study site for > 5 months. Large Suwannee cooters can be highly vagile and are capable of covering long distances rapidly (> 1.5 km in a day), with few individuals found > 5 km from previous capture locations. For large turtles, the propensity to move across different habitats and the size of the actively used linear home range varied extensively and were best explained by individual variation rather than by sexual differences. We observed an abundant population, including all size classes. Turtle distribution throughout the site was unequal among river sections and was positively correlated with the number of basking sites and water depth. We recommend basking counts to monitor population trends in blackwater rivers, especially under conditions of high tannin concentrations when hand capturing turtles is difficult.