Even in situations where the influences of non-native species are reasonably well known there is large potential for climate-change and other drivers to substantially alter those effects because of contingencies driven by river dynamism. We review how network connectivity and disturbance regimes likely control the influences of non-native trout on vulnerable native galaxiid fishes in Aotearoa New Zealand. Firstly, disturbances, like flooding or drying, generally affect trout more than native non-migratory galaxiids, often leading to small increases in galaxiids released from strong predatory interactions with trout in disturbed reaches. Such galaxiid increases have sometimes been misinterpreted, but when properly controlled, comparisons across disturbance gradients reveal deleterious effects of both trout and environmental harshness on galaxiids. Secondly, the differential disturbance-driven reductions in trout and galaxias likely alter the balance of processes affecting galaxiid populations with trout predation becoming less important, and trait-mediated effects becoming more important. For example, low density trout may drive growth advantages for galaxias, most likely through trout-induced changes to invertebrate behaviour indirectly benefitting galaxias. However, long-term effects on galaxias growth rates under such scenarios are unknown and we need to evaluate how the balance of predatory interactions compares to any trait-mediated effects. Finally, disturbance influences play out across heterogenous riverscapes, and likely involve source-sink population dynamics, metacommunity processes and depend on galaxiid life history. Confluence heterogeneity (i.e. combination of stable and disturbed branches) can promote interaction stability, for example, but we don’t understand the dynamics that drive that and how life history differences and stream conditions might affect any coexistence mechanisms. Thus, overall, interactions between trout and galaxiids are far from the settled ‘equilibrium’ sometimes suggested, and both disturbance regimes and network configuration have a large influence. We need to better understand this dynamism to guide management actions in a very uncertain world.