Lagoon of Islands
Lagoon of Islands Rehabilitation Project
Located in Tasmania’s central highlands, this unique ecosystem characterised by floating islands of terrestrial vegetation was flooded by Hydro Tasmania in 1968 to deliver irrigation water to downstream irrigators along the Ouse River and offset water releases from Great Lake.
Downstream demand exceeded the capability of the natural catchment and in 1984 Ripple Canal was constructed to divert a number of small tributaries of the Shannon River to the lagoon. Though substantially increasing the yield from the lagoon this action proved to be ecologically disastrous as the canal also contributed large volumes of nutrient rich water ultimately resulting in a collapse of the natural system and unacceptable water quality.
Low inflows in recent years combined with the poor environmental conditions have prevented any water releases for irrigation purposes requiring expensive releases from Great Lake to occur.
Addressing the issues at Lagoon of Islands is one of the key objectives of the Ouse River Project that aims to resolve a number of inter-related water related issues in this area. Construction of alternative water supply infrastructure for Ouse River irrigators is being progressed and, once commissioned, will render Lagoon of Islands redundant and allow for the dam to be decommissioned and the water body to be rehabilitated.
A panel of internal stakeholders and external experts was assembled to advise on the best course of action to improve the poor environmental conditions persistent in the lagoon. In May 2010, the first major action was taken with the decommissioning of Ripple Creek Canal. Four tributaries artificially flowing into Lagoon of Islands were redirected back to their natural course and into the Shannon River. The dam wall is currently being deconstructed to allow for natural water levels to occur. Read more here >
Further interventions are being considered but will depend on the lagoon’s response to removing the canal and dam. Full recovery of Lagoon of Islands to its original state is unlikely in the short to medium term. However, Hydro Tasmania is confident that the approach will see improvements in water quality in the short-term and set the lagoon on the best path to long-term recovery.