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| LakesTasmania has an abundance of lakes, including the continent's largest permanent natural freshwater lake, Great Lake, and the deepest, Lake St Clair. These lakes are created and shaped by geological, geomorphic, and other processes.
 Glaciation created many of Tasmania's lakes. Glaciation scoured bedrock troughs, and basins formed from glacial till, that are widespread in the Tasmanian highlands and the Central Plateau. Lake St Clair's depth is due to both these processes.
Arid, windy conditions during the glacial periods created many wind-scoured hollows in the Midlands and east of the State. Many of these hollows became inland lakes and wetlands.
The physical structure of the water mass in lakes tends to show characteristic patterns - such as undergoing a yearly cycle of stratification and mixing.
During stratification, the water mass separates into layers of different densities. Stratification is frequently accompanied by the development of biological, physical and chemical zonation.
Some highland lakes in Tasmania are dimictic - stratifying in summer and winter and overturning in the spring and autumn.
Most Tasmanian lakes have irregular mixing cycles (polymixic), or are completely mixed all year round (holomixic) but there are a few examples of permanently stratified (meromictic) lakes in Tasmania.
Lakes and wetlands are generally low - energy depositional environments characterised by still water and soft, muddy bottoms.
In the low - energy lake environments, sediments and nutrients accumulate. This means that the flora and fauna throughout the aquatic and riparian environments tend to be more diverse and abundant in these systems than in streams. For example, the phytoplankton population (all photosynthetic plankton including unicellular algae and cyanobacteria) is unusually large. However, water depth is very important. If a lake has an extensive deep zone where the water may be dark, cold or oxygen deficient, the benthic population living on the bottom of the lake can be small. The opposite is usually true in shallow lakes and wetlands.
Reference: SDAC 1996: State of the Environment Tasmania, Volume 1 - Conditions and Trends, compiled by the State of the Environment Unit, Land Information Services, DELM, Tasmania.
Photograph copyright Tourism Tasmania
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