There has been considerable debate over the interaction between longwall mining subsidence and loss of flow in stream systems. Upland swamps on the Woronora Plateau provide significant baseflow to the streams of the Sydney Drinking Water catchment. In recent times however, a number of upland swamps have been significantly impacted by longwall mining, leading to the loss of perched aquifers within these swamps. This has then led to the near complete loss of flow in the stream channel immediately downstream of such swamps. Such impacts potentially have important consequences for a variety of aquatic organisms including a range of threatened species. In anticipation of mining affecting a number of these swamps, a before-after-control-impact-(BACI) research program was implemented to look at the impacts of longwall mining on upland swamp aquifer levels and their subsequent flow delivery to streams. Preliminary results from this research program demonstrate a relative loss of water within the first swamp to be undermined, a flashier response in terms of stream flow after impact and a much faster drying up of the swamp’s peaty sediments. These preliminary results are contrasted with the behaviour of nearby reference swamps which have not been undermined. The implications of such research suggest that longwall mining can have serious impacts on the surface and groundwater hydrology of the Woronora Plateau. Such impacts are likely to have important flow-on effects to aquatic species and downstream users.