The true nature of our environment is one of constant change and flux. It is dynamic, and there is no such thing as stability. Human beings have tried to make the environment more stable by technology and in doing so we have created the false expectation that things will always be the same as we have come to expect.
In the case of the River Murray, up until the last couple of years, the locks have kept more or less constant water levels, which has been handy for irrigation and drinking water, but it certainly was not like this previous to the locks. The Lower Lakes levels have been kept artificially high by the barrages, as can be plainly seen by the fences that go out into the area of the old Lake. The true original natural state of the River and Lakes was one of constant flux, sometimes of huge floods, and other times of drought leading to the River being a series of pools, which is what it would be like now if the locks hadn’t been put in. During the drought times the sea would have made significant incursions into the Lakes, as happens in an estuarine situation. We don’t really know how long some of these drought situations may have lasted, perhaps decades or even centuries. We also don’t know how far the seawater may have coursed up the River, quite possibly much further than has previously been acknowledged in indigenous memory.
Another aspect of the debate that needs attention is just what is “natural”. We all have our pet theories about what it is, depending on our particular priorities. For instance, acid sulphate soils are natural. They arise from the exposure to air of soils which have previously been covered with water, a natural occurrence in time of drought. The sulphides in the soil, remaining from previous incursions from the sea in the geologically distant past, become oxidized and produce sulphuric acid. So to try and neutralize these soils with agricultural lime, were it possible on such a large scale, is actually unnatural. We don’t want the acid for our human needs, so we label it as unnatural.
This type of argument is also used to justify keeping the lakes fresh, however, permanently fresh Lakes are unnatural, since the natural state is alternating fresh and saline, a fluctuating estuarine state. Similarly, permanently saline Lakes would also be unnatural, and particularly so since it would be preventing the formation of sulphuric acid, the natural situation.
We must weigh up the alternatives of several unnatural situations and decide what is best for the environment.