Great Lake is currently at 11.4 per cent capacity, and has fallen 2.5 metres below its September 2015 mark.
Hydro is still feeding water from the lake to the Poatina Inlet power station as the state deals with a power crisis.
The lake is currently classified as a high environmental risk zone prompting environmentalists to urge Hydro to stop draining the lake.
Tasmanian Conservation Trust director Peter McGlone said wildlife in the area was at risk.
Published by: ABC News, 10/3/2016