The distributary creeks of the alluvial fan of the lower Lachlan River (NSW) are dotted with flood-out wetlands. Some of these have a distinctive internal topography, dominated by dense River Red Gum forest-woodland. The unique nature of these mound-channel wetlands has only recently been recognised, and their geomorphic origins are not established. Murrumbidgil Swamp, an example of these, was the site for landmark ecological studies on productivity, waterbirds and wetland ecology during the late 1970s. The knowledge gained from these studies and since then suggests strongly that the unusual ecological character, distinctive habitat, and productivity of Murrumbidgil Swamp are due to three primary factors: internal topography, the density of majestic mature-veteran River Red Gums, and the controlling influence of flow regime. Two condition assessments in the last six years of Murrumbidgil Swamp and another mound-channel wetland show that this character has undergone a dramatic change, due to changes in water regime. The combination of the Millenium Drought and river regulation followed by extensive and persistent floods, have resulted in extensive dieback and death of established trees, followed by widespread regeneration. It is postulated that it will take decades for Murrumbidgil Swamp to attain the ecological character it had in the 1970s, and that the likelihood of such a recovery is uncertain, due to the character being dependent on maintaining a certain type of water regime. This paper will describe the condition and population structure of River Red Gums at two points in time, March 2007 during the Millenium Drought and October 2013 after the floods; compare these with condition in 1975-1981, inferred from historical and informal sources; and present a conceptual model of the controlling influence of water regime to look forwards to the 22nd century.