The Causeway Lake having an area of about 86 ha represents an artificially created lake in the estuary having restricted connection with the sea by the bridge width and bridge sill elevation. It is located on the Capricorn Coast, Queensland. The lake is a sink for suspended sediment transported from the sea by the tidal currents as well as for sediment transported from the catchment by the creeks when the intensity of the rainfall is sufficiently high. During 65 years, since the lake creation, the siltation significantly reduced usability of the lake as a recreational area for fishing and sporting activities. It is no longer accessible by yachts or motorboats because of the large area of the lake which has a depth below 0.5m. The report discusses the sources and progress in siltation of the lake. The probable quantities of the sediment entering the lake from the sea and from the catchment were estimated.