Coastal lagoons and estuaries in southeastern Australia mainly occupy lowstand incised valley systems that have been impounded by post-glacial sea-level rise. Most previous research has focused on larger estuarine and deltaic systems but the Swan Lake deposits record the geomorphic evolution of a small perched saline coastal lagoon that has remained in a youthful stage of estuary infilling with very slow progradation of the bayhead delta and slow accumulation of the central basin mud facies. This can be attributed to the relatively small catchment that is covered with natural vegetation. Marine influences at the flood-tide delta have been restricted by the perched nature of the lagoon and the high wave energy on the coast that rapidly closes the entrance with sand. Comparison with other similar lagoons along the NSW coast between Sydney and Batemans Bay illustrates the general geomorphic evolution of saline coastal lagoons. Such lagoons are also very similar to small perched lagoons in South Africa and to a lesser extent with those on the east coast of South America.