The cohesive sediment transport in tidal rivers and estuaries is determined by the river discharge, the morphology, the salinity, temperature and particulate gradients, the deposition and erosion processes, the effective settling velocity of mud particles and by the physico-chemical and biological processes. The combination of these processes ensures that mud concentration varies on different time-scales ranging from seconds to seasons. Based on a long-term measurement campaign at Prosperpolder (Scheldt Estuary, Belgium), a detailed analysis of mud concentration, salinity, temperature and freshwater discharge with regard to the various involved time-scales is presented. The measurements at Prosperpolder were carried out between September 1992 and December 1993 at 0.5 and 1.5 m from the bottom. The data indicate that the mud concentration is correlated with tides, spring-neap cycles and with seasons. The mud concentration in Prosperpolder is on average higher during flood than during ebb, which can be explained by the flood dominant character of the currents. The tide averaged mud concentration is 1.3-1.7 times higher during a spring tide than during a neap tide. The ratio between the winter and summer concentration is about 2. The seasonal variations are due to the river discharge (transport, shift of the turbidity maximum), temperature (biological activity, climatological factors) and land erosion (terrestrial input of fine sediments).