In the last few days I had to drive along the eastern shore of Lake George in southeastern New South Wales. It is called Weereewa in the Indigenous language of the area. The lake is roughly subtriangular and at 25 kilometres long and 10 kilometres wide is quite a decent size. Given its size, it is quite shallow, with its maximum depth only being about 7.5 metres and its average depth only about 1 metre1. The lake is what is called an endorheic lake, in that its drainage system is closed such that there is only inflow, and no surface outflow2. There are numerous endorheic lakes in Australia, with Lake Eyre being the largest3.
The water level in the lake is higher than I have seen for quite some time. Several times in the last decade, I have driven past its western shore and could barely see any of the water in the lake, as it was only on the eastern side, which is the deepest part of the lake. However, this time, the water was near the foundations of the highway along the western shore in some places.
There have been all sorts of stories supposedly explaining why the water level in the lake varies so much. These included the extremely fanciful underground ‘tunnel’ connection, under the Tasman Sea, with Lake Taupo in New Zealand because it was ‘well established’ that when Lake George’s water level was low, that in Lake Taupo was high. How this story came about is now unknown4. However, we now know that it is mostly a matter of inflow versus evaporation which determines the lake level. The current filling of the lake is because there has been a La Niña in operation over the last few months. La Niña events increase the chances of above-average rainfall for northern and eastern Australia during spring and summer5.
That is where we are now. As the La Niña declines, as it seems to be doing, the water level in the lake will decline with it, as the rainfall in the area decreases.