Have you ever heard of a perched lake? Perhaps you have been lucky enough to visit one but didn’t realise just how special it really is? For me, a recent visit to one of these amazing lakes, Lake Poona near Rainbow Beach, has inspired me to want to learn more!
Perched lakes are also known as coastal dune lakes and can be found dotted along Queensland’s coast from Cape York to the NSW border. One of the things that makes these lakes truly special is the fact that they manage to form on the siliceous sands of the dune systems which are usually devoid of streams or water bodies because water so quickly filters through the sand into the groundwater.
So how do perched lakes form?
A perched lake forms in a depression in the coastal dune landscape where organic matter has been deposited over time and has decomposed into the top layer of sand, effectively ‘cementing’ it together to form a crust. This layer then begins to slow down the infiltration of water through the sand and so trapping water above the ground to form a lake which can be many metres above sea level.
The freshwater found in these lakes can appear crystal clear or is often stained brown by the tannins leached from the surrounding vegetation, especially tea-trees and paperbarks. The water also tends to be quite acidic (with a pH of 6 or lower) and is quite low in nutrients. Despite this these lakes often support a rich diversity of macro invertebrate life as well as the varied vertebrates that rely on these creatures for food, such as frogs, fish and many birds.
DID YOU KNOW? More than half of the world’s perched lakes occur right here in Queensland including some of the best examples on Fraser Island – the world’s largest sand island. In fact the largest perched lake in the world, Lake Boomanjin, is found here.
Queensland’s amazing freshwater coastal lakes are also critical habitat for some of our unique and rare species such as the Wallum Froglet (Crinia tinnula), the elusive Ground Parrot (Pezoparus wallicus) and the beautiful and distinctly Australian Christmas Bells (Blandfordia grandiflora).
Have you ever visited one of these incredible lakes? Take a look at these websites and go and explore one for yourself:
Coastal and subcoastal non-floodplain sand lake—Perched – Locations, WetlandInfo, Department of Environment and Heritage Protection, Queensland, viewed 27 September 2017, <https://wetlandinfo.ehp.qld.gov.au/wetlands/ecology/aquatic-ecosystems-natural/lacustrine/non-floodplain-perched-lake/location.html>
Natura Education (2016) ‘Waterways Field Guide – Series 2: Water Habitats’ An initiative of Gold Coast Waterwatch and supported by City of Gold Coast
Christmas Bell image by Ryan Hughes
All other images by Dionne Coburn