Restoration of Lagoon of Islands

02 February 2021

Dr Carolyn Maxwell, Climate and Water Strategy Specialist

In a state abounding with natural beauty, the casual observer may say Lagoon of Islands is unremarkable, but to an ecologist Lagoon of Islands is a place of wonder.


Nestled near Woods Lake on the Central Plateau, the 9 square kilometre wetland, Lagoon of Islands, does not attract a lot of attention, but it was once a ‘floating wetland’ unlike any other in the world.


Once, ti-tree, eucalyptus, bottlebrush and sedges formed pockets of vegetation that were rooted on a mat of reeds which floated on the surface of this wetland. The roots of the reeds were secured into soil at the edges. Floating wetlands are uncommon globally, but Lagoon of Islands had species known only to live in Tasmania, making it unique in the world.


In the 1960s, the then-Hydro Electric Commission diverted water from Waddamana Power Station into the new Poatina scheme, so people downstream needed an alternative source of irrigation water and in 1964, Lagoon of Islands was dammed. Rising water levels flooded the wetland beyond the ability of the reed mat to respond and the wetland vegetation slowly died.


World Wetlands Day_Former Hydro Tasmania water monitoring site at Lagoon of Islands


The decline of the ecosystem was recorded in a case study by Tasmanian ecologist, Professor Peter Tyler. His work later joined a body of scientific evidence demonstrating the destruction of wetlands around the world, which eventually supported an international instrument to protect wetlands, the Ramsar Convention on Wetlands.


Boom and bust

As the plants in Lagoon of Islands died, these provided nutrients that super-charged the food chain and made the area a popular trout fishery. The construction of Ripple Creek Canal in 1984 provided more water for downstream users and more nutrients from decaying vegetation. The water quality slowly deteriorated as the ecosystem could no longer use all those nutrients and the fishery soon declined.


World Wetlands Day. A satellite image of Lagoon of Islands, the bright green blob, as seen from the sky.


Satellite images from 1988 show the lagoon as bright green, with a severe algal bloom. The poor water quality reached its peak when the 2006-8 drought hit the region. Hydro Tasmania’s storages reached low levels not seen since the 1960s. It was no longer water that flowed downstream from the lake, but a gurgling and slurping sludge not fit for irrigation or domestic use.


Nature finds a way

Bold action was needed to restore good water quality to Lagoon of Islands and nature already hinted at the answer.


Around the start of the millennium, isolated green spears of vegetation began to emerge. As the drought intensified and the water level dropped, a few spears turned into a handful and then into noticeable clumps, which remained alive when the drought broke.


Thankfully, Professor Tyler had continued his interest and recognised their significance immediately: Baumea arthrophylla or ‘fine twig-sedge’. This plant was a key foundation of the wetland’s reed mat before it was flooded and it was now re-colonising the lagoon. This created the possibility of a restoration plan. Maybe, if we could reinstate the natural patterns and depths of water in the lagoon, just maybe, the ecosystem would recover.


The restoration

Hydro Tasmania decommissioned Ripple Creek Canal in 2010, and the restoration of Lagoon of Islands commenced in 2012, as the lake was drained in preparation for dam removal.


The clay that formed the dam was contoured into the landscape and rocks from the dam were used to line the new creek channel. Guided by a panel of experienced scientists, we attempted to mimic the behaviour of water in the wetlands before it was dammed.


World-Wetlands-Day_An aerial-view-of-Lagoon-of-Islands


We saw and measured immediate improvements in water quality, with water now suitable for use by people downstream of the lagoon. Fine twig-sedge and other plants continue to recolonise the lagoon.


The success in restoring Lagoon of Islands has been demonstrated in a new scientific paper, published in the latest volume of Ecological Management and Restoration, which shows the gradual re-emergence of a healthy, self-sustaining and biodiverse wetland.


During his work, Professor Tyler would often quote Roman poet, Horace - Naturam expelles furca, tamen usque recurret – “You may drive out nature with a pitchfork, but she keeps on coming back”.

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