A mathematical model is proposed for the movement of water and sediments in Coral Creek. a tidal creek surrounded by thickly vegetated mangrove wamps in Missionary Bay at the northern end of Hinchinbrook Island, northern Queensland. It is shown that a net down-stream longitudinal current through mangrove swamps exists and is responsible for rapidly carrying away organic detritus (e.g. fallen tree leaves) to the ocean, thereby enhancing the export of nutrients from mangrove swamps. The asymmetry between ebb and flood currents contributes to the maintenance of a deep self-sustaining drainage channel. even in the presence of a large sediment input from surrounding coastal waters. The size and geometry of the drainage channel are related to vegetation density in mangrove swamps. Evapotranspiration from mangroves in Coral Creek is responsible for the existence of a longitudinal salinity gradient. The evapotranspiration rate could be as large as 3 cm,'day. Residual currents are clockwise in Missionary Bay and explain the overall patterns of scour and deposition in the bay.