Lake Fidler is a small meromictic lake on the lower Gordon River floodplain. Since the commissioning of Hydro Tasmania’s Gordon Power Station in Tasmania’s south-west, the freshwater flows to the Gordon estuary have increased, reducing the incidence of upriver saltwater intrusion. This has also reduced the incidence of saltwater recharge into the lake.
Meromictic lakes are characterised by a stable structure of an oxygenated freshwater upper layer over an anoxic saline lower layer, and are rare worldwide.
Lake Fidler has been listed on the Tasmanian Wilderness World Heritage Area as containing significant values associated with its unique limnology and biota. With reduced saltwater recharge events, the anoxic lower layer in Lake Fidler (the monimolimnion) became slowly more dilute, to the point where Lake Fidler became in danger of losing its permanent meromictic nature.
In 2004, Hydro Tasmania acted to halt the reduction in salinity by recharging the lake with saline water to increase the lake’s meromictic stability and protect the lake’s unique biota and fossil record. As there was no precedent for this type of lake management, several limnological and water modelling studies were undertaken and specialist limnologists consulted.
Results obtained from monitoring the status of meromixis in Lake Fidler in 2007 have indicated that the Lake continues to be salinity stratified, however, despite the artificial recharge continued reduction in conductivity is occurring. Monitoring is continuing.