Across much of its range, the river cooter is active from April to October, hibernating in the mud or on the bottom of its watery habitat during cold winters. However, in warmer winters this species may remain active year round (2). The river cooter is mostly diurnal, foraging underwater in the early morning and late afternoon (2) and spending much of the rest of its day basking in the sun with other individuals of its kind (2) (3) (4) (5).
The adult river cooter is a primarily herbivorous reptile, eating a variety of plants and algae (1) (2) (3) (4) (5), while the young of this species are omnivorous (5), also feeding on snails, crayfish, insects, tadpoles and small fish (2). However, adult river cooters may occasionally supplement their diet with animal prey (2). As an adult, the river cooter has very few natural predators, but nests are often raided by fish crows (Corvus ossifragus), raccoons (Procyon lotor) and grey foxes (Urocyon cinereoargenteus) (2).
The age and size at which maturity is reached in the river cooter varies slightly with location (1) (2), although typically males become sexually mature at about 6 years old and females between 13 and 24 years old (1). Mating in this species occurs in the spring (2), and courting involves the male swimming with and above the female, vibrating its claws in her face (5). The nesting season lasts from May through to the end of June (2) (3), with nesting typically taking place during the day (3), usually not far from the river (2) (3).
The female river cooter digs a flask-shaped nest cavity using only her hind feet (2), within which around 20 eggs are laid (2) (4) (5). The eggs are incubated for a period of between 70 and 96 days (1) (2) depending on the temperature of the soil (2), typically hatching in August or September (2) (5). The temperature of the soil also determines the sex of the hatchlings. At incubation temperatures of between 22.5 and 28 degrees Celsius, the clutch will contain mostly males, whereas at temperatures of 29 degrees Celsius and above, females will be produced (2). Female river cooters produce up to six clutches per year (1) (2), although two is most common (2), and individuals of this species are thought to live for up to 40 years (1).