Lake Alexandrina lies at the end of the Murray Darling Basin. The 7000 year diatom record from core LA2 reveals that Lake Alexandrina was strongly influenced by tidal waters during the 5000-2200 year BP dry phase but these were relatively rare after as regional climates once again became humid. That said the greatest change in the condition of Lake Alexandrina over the last 7000 years was to a freshwater state which occurred after the commissioning of the barrages after 1940, which controlled the tidal flux, although 1946-76 was also characterised by an extended wet phase. At the time of its listing as a Ramsar site in 1985 it was described as being mostly fresh and this was reinforced in 2004 where it was described as being ‘predominantly fresh’ prior to European settlement based on anecdotal accounts. Saline invasions were considered unusual prior to 1900 and locals lamented the increasing salinity from 1902. This was attributed to drought and the increasing diversions in the upper course of the Murray and drove the decision to commission barrages from 1935-40 to prevent the inrush of salt water. The rainfall reconstruction from 1788 to present for south-east Australia (SEA) reveals the Interdecadal Pacific Oscillation to have been mostly negative in the 1800s driving a long term positive rainfall anomaly across SEA. This abruptly turned positive in 1899 driving a drought dominated phase through to 1945. As diversions were much lower than today, these anecdotes likely reflected a stepped change in climate. From 1997-2008 Australia experienced its worst historical drought at the end of an extended drying phase over millennial time frames. Historically, under these conditions (and those that lie ahead) the natural state of Lake Alexandrina would be a variable fresh-tidal system. The ongoing use of the barrages to prevent the inflow of marine water, even in extreme drought, and the allocation of scarce and highly contested fresh water flows to preserve a freshwater state ignores the multi-scale variability in the long term natural character of the lake and the prevailing influence of climate in regulating the interplay between fresh and marine waters.