The Itaipu Lagoon, located in Niteroi, Rio de Janeiro State, was deeply affected by urbanization during the 70's and 80's, causing major geomorphologic changes. Dredging of the lagoon bottom and reopening of the tidal inlet in 1979 caused lowering of water level with consequent reduction of the wet area. Comparison of aerial photographs taken in 1976 and 1996 quantified in 33.9% the reduction in water surface. Bathymetric survey indicated that 80% of the lagoon bottom is flat and very shallow (around 1 meter deep). The shallow areas are covered with mud derived from the drainage, which is accumulating at a rate of 0,28 cm/year for the last 100 years, based on 210Pb analyses. Deforestation and human occupation of drainage and lagoon margins accelerated the shallowing up of the lagoon. Other morphologic features are a 6-meter deep dredged channel and a flood tidal delta. Sands coming from the beach and nearshore zones trough the tidal inlet are concentrated by present-day lagoon hydrodynamics along the deep channel and on the tidal delta, where sand is moderately sorted. Tides generate a clockwise circulation within the lagoon with current velocities between 0.02 to 0.3 m/s and up to2.47m/s in the inlet. Tidal currents and sporadic storm waves are responsible for transport, removal and distribution of the sands on the lagoon bottom.