Sauropod dinosaurs were the largest terrestrial animals to have ever existed, and are difficult to interpret as living animals owing to their lack of living descendants. With computer models that employ the basic physics of buoyancy and equilibrium, it is possible to investigate how the bodies of these animals would have reacted when immersed in water. Multi-tonne sauropods are found to be extremely buoyant and unstable in water when aspects of their probable respiratory anatomy are considered, which obviates the old problem of them being unable to breathe when fully immersed. Interpretations of 'manus-only' trackways made by floating sauropods will depend on the details of buoyancy as not all sauropods float in the same manner.