In subtropical climates where evaporation is likely to exceed the supply of freshwater from precipitation and river run-off, large coastal bays, estuaries and near shore coastal environments are often characterized by inverse circulations and hypersalinity zones. An inverse circulation is characterized by sub-surface flow of saline water away from a zone of hypersalinity towards the open ocean. This flow takes place beneath a layer of inflowing oceanic water and leads to salt injections into the ocean.
In the movie below we show some model results to "proof" that Hervey Bay is such an inverse bay. One can see that during summer (the australian one), near the coast a hypersalinity zone forms. During winter the salinity gradient is due to higher precipitation/less evaporiaton weakend. Also shown in the movie is a flood event. Here the Mary River (at the southern end of Hervey Bay) flushes a significant amount of freshwater into the bay. Therefore the inverse state of Hervey Bay flips over to a regular one (the salinity near the coast is lower than in the open ocean). With the approach of winter, the evaporation starts to reduce the freshwater content of the bay and again the inverse state is established.