Knowledge of the relationship between river flow and wetland inundation at a reach-scale is important for effective flow management, particularly, for environmental outcomes. Historical remotely sensed data, such as Landsat TM, provide the potential to determine the relationship between flow and wetland inundation for extended river reaches. In this paper we apply, adapt and evaluate a technique using sets of before-flood and after-flood image pairs to relate river flow to wetland inundation on a 640 km reach of the mid-Murrumbidgee River, Australia. Stratification of the complete reach into relatively uniform sub-reaches on the basis of hydrology and geomorphology was undertaken as a key pre-analysis step. Analysis of flood wave attenuation within each sub-reach showed that flood peaks entering and leaving a reach were highly correlated. Therefore, we argue that a flood peak measured at a single gauge within the reach can be used to provide a reliable indication of the behaviour of similar sized floods within the reach. The remote sensing technique proved capable of producing a model relating wetland inundation thresholds to flood peak discharge for each sub-reach within the extended river reach. Although the model simplifies the complex relationship between river flow and wetland inundation, reliable key wetland inundation flow thresholds were determined.