What causes Lake’s George’s water levels to fluctuate so wildly?
ACCORDING TO this far-fetched, yet surprisingly oft-touted, theory, the water levels in Lake George, an ephemeral body of water located between Goulburn and Canberra, “go up as the water levels in [insert random name of another lake in China or Siberia] go down, and vice versa”.
Of course, any suggestion freshwater lakes in different hemispheres are linked is fanciful rubbish. So just what does cause the lake’s fluctuating levels, which have mystified many travellers since ex-convict-come-explorer Joseph Wild first set eyes on this “inland sea” on 19 August 1820, to fluctuate so wildly?
In the 200 years since Wild’s visit, the lake, which, when full, has 60km of shoreline, making it the largest freshwater natural lake in inland New South Wales, has completely filled and emptied on numerous occasions.
Despite the proliferation of theories to the contrary, various studies have proven that the shallow lake – 6m at its deepest and with an average depth of 2.5m when full – fills and empties purely as a result of rainfall and evaporation.
It can take several years of above-average rain for the lake to be filled by five small creeks that empty into it, but, resembling a large shallow saucer, and with no outlets, the lake can dry out quickly during a hot, dry summer.
While the myth that Lake George’s water levels are connected via a network of subterranean funnels to other lakes around the world is, dare I say, blown out of the water. Explaining just how the lake’s water levels can also appear to vary on the same day is a little more tricky.
William Glover, a meteorologist based at the lake in the 1890s, recorded the water level temporarily falling almost 500mm in one day.
This sudden variation, which continues to mystify modern-day travellers, is explained by the prevailing winds. By day, the wind usually blows from the west, and, because the lake is shallow, a strong wind can blow the water towards the eastern side of the lake. At night, the wind is often an easterly, which simply blows the water back to the other side. This phenomenon, which occurs in some other lakes around the world, including Lake Geneva, between Switzerald and France, is called a seiche.
Governor Macquarie named the “noble expanse of water” after the reigning monarch King George IV. There is now a move to refer to the lake by its Indigenous name of Weereewaa, which, according to Ngambri elder Shane Mortimer, means “place of many migratory birds”.
Recent rains have filled the lake to its highest level in years. If this continues, one thing is certain: it will be due to a wetter-than-average summer, and not water mysteriously gushing down some subterranean funnel from Siberia.