This chapter describes an example of an inverse estuary, Spencer Gulf in South Australia, outlines models based on the water and salt balances, and also describes dynamical models which have been applied to Spencer Gulf and its outflow. The maximum density at the head of the gulf, and the maximum longitudinal density gradients occur in April/May, that is, in winter. The strongest convective circulation might be expected when the density difference between the estuary water and the water outside the mouth is greatest. Notice that in both the wind-driven and convective models there is a removal of water, as well as salt, from the estuary by the outflowing current, a feature which is not normally present in the advection-diffusion models. The salt balance requires that over a sufficiently long period of time, the advection of salt into the estuary is balanced by an efflux of salt.