Factors influencing deoxygenation following an unintended whole of water body herbicide treatment of aquatic weed cabomba in a natural wetland in the Blue Mountains, NSW, Australia

![CDATA[Glenbrook Lagoon, an eight hectare natural escarpment wetland in the Blue Mountains of New South Wales, has a history of poor water quality and aquatic weed infestations because of the surrounding urban catchment. Until recently, the lagoon was densely infested with cabomba (Cabomba caroliniana), an invasive aquatic weed listed as a Weed of National Significance (WoNS). In December 2012 the cabomba infestation was successfully treated using the recently registered SharkTM Aquatic Herbicide (240g/L carfentrazone-ethyl) (Shark). The application was intended to treat only 50% of the water body (as per label directions), but was found to be effective in controlling cabomba across the entire water body. Oxygen depletion was observed across the entire water body following the rapid dieback and decomposition of weeds, together with other contributing factors including stratification and warm, still prevailing weather conditions. A fish kill of stocked Australian bass (Macquaria novemaculeata) occurred after a prolonged period of extremely low oxygen levels (0.04%; 0.4 mg/L). Attempts to re-oxygenate the 8 ha lagoon were largely unsuccessful. Case studies of cabomba control in large natural water bodies in Australia using aquatic herbicides are rare and this paper seeks to outline some of the challenges involved, the lessons learned and make recommendations on how to implement a successful control program whilst minimising deoxygenation.]]