Some estuaries have relatively low suspended sediment concentrations of the order of 100 mg/l, while others are hyper-turbid, with sediment concentrations up to several tens of grams per litre. Over the last decades we also have seen estuaries, such as the Ems and Loire, where a transition occurred from a low to a high concentration, possibly due to human interventions in the estuarine system. Such a regime shift can potentially have devastating effects on the quality of the ecosystem. Winterwerp and Wang (2013) hypothesise that the low and high concentration conditions may both be equilibrium states of an estuary under the same forcing conditions. In this presentation we will test this hypothesis and investigate the behaviour of the most essential physical processes. This is done using a numerical water column model.