Expansion of opportunistic species such as Phragmites australis (Common Reed) following changes in water regimes, climate and physical disturbances is a process challenging wetland managers globally. At Johnson Swamp, a freshwater floodplain wetland in north-western Victoria, altered water regimes have coincided with the expansion of Common Reed and Duma florulenta (Tangled Lignum). Although both species are native to Victoria and provide important habitat, their expansion can locally diminish other vegetation communities and lead to a shift in vegetation state viewed as undesirable. We monitored vegetation responses to slashing with and without herbicide followed by inundation for 31 months by environmental water delivery and natural inflows, and a repeated application of slashing with and without herbicide without subsequent flooding. We established 21 quadrats across the different vegetation types and treatments, including controls with flooding only. Environmental water delivery and natural inflows alone did not control either species. Common Reed cover and stem density were temporarily reduced by both slashing-only and slash-herbicide treatments, though extent was not reduced and eradication within the treatment areas was not achieved. The regrowth of Common Reed stems following treatment suggests it will regrow to pre-treatment density and reverse these changes. Tangled Lignum was greatly reduced in cover, in some cases to zero, within both slashing-only and slash-herbicide treatments, but we also recorded Common Reed in treatment quadrats where it had not previously appeared. Our findings suggest that slashing is unlikely to effectively control fast-growing, disturbance-adapted species such as Common Reed, even when followed by extended inundation. Without remediation of altered water regimes, landform or other underlying processes driving dominance, the same species are likely to return. Where remediation is not possible, land managers may need to accept some level of change in vegetation state and set objectives accordingly.