15 The shallow tidal and freshwater coastal wetlands adjacent to the Great Barrier Reef lagoon 16 provide a vital nursery and feeding complex that supports the life cycles of marine and 17 freshwater fish, important native vegetation and vital bird habitat. Urban and agricultural 18 development threaten these wetlands, with many of the coastal wetlands becoming lost or 19 changed due to the construction of artificial barriers (e.g. bunds, roads, culverts and 20 floodgates). Infestation by weeds has become a major issue within many of the wetlands that 21 were modified (bunded) for ponded pasture growth last century. A range of expensive 22 chemical and mechanical control methods has been used to try and restore some of these 23 coastal wetlands, with limited success. This study describes an alternative approach to those 24 methods, investigating the impact of tidal reinstatement after bund removal on weed 25 infestation, associated changes in water quality, and fish biodiversity, in the Boolgooroo 26 lagoon region of the Mungalla wetlands, East of Ingham in North Queensland. High resolution 27 remote sensing, electrofishing and in-water logging was used to track changes over time -1 28 year before and 4 years after removal of an earth bund. With tides only penetrating the 29 wetland a few times yearly, gross changes towards a more natural system occurred within a 30 relatively short timeframe, leading to a reduction in weed infestation, reappearance of native 31 vegetation, improvements in water quality, and a tripling of fish diversity. Weed abundance 32 and water quality does appear to oscillate however, dependent on summer rainfall, as 33 changes in hydraulic pressure stops or allows tidal ingress (fresh/saline cycling). With an 34 estimated 30% of coastal wetlands bunded in the Great Barrier Reef region, a passive 35 remediation method such as reintroduction of tidal flow by removal of an earth bund or levee 36 could provide a more cost effective and sustainable means of controlling freshwater weeds 37 and improving coastal water quality into the future. 3 38 39 Introduction 40 Coastal floodplains around the world have been modified for human gain, most notably being 41 hydrologically altered either totally or partially reducing connectivity between floodplains and 42 coastal areas [1, 2]. Floodplain, coastal tidal and freshwater wetlands are important habitat 43 because they provide important biodiversity, hydrological, cultural and economic goods and 44 services [3-5]. However, these wetlands are under great pressure due to urban and industrial 45 development [6, 7] or agricultural and grazing land expansion, with many coastal wetlands 46 becoming lost due to the construction of artificial barriers (e.g. bunds, roads, culverts and 47 floodgates) which have stopped or reduced tidal flushing, negatively impacting aesthetic and 48 ecological values [8]. The widespread degradation of coastal wetlands has led to major shifts 49 in species assemblages and declines in aquatic species productivity. In response, the...