The Queenstown Lakes District Council pulled the pontoon from the water in February, because it was continually being tipped over by swimmers overcrowding the floating structure.
The oblong pontoon was put back in the water yesterday at the Lake Wanaka marina.
QLDC engineer Rob Darby said flotation and stability tests would be done today before the pontoon was returned to its former location near the town's old wooden jetty.
Mr Darby said buoyancy changes should stop the pontoon from being tipped over.
Builder Brian Shaw said he had added an extra layer to the structure to counteract the effects of "negative buoyancy", which had contributed to the pontoon's tipping point when it was submerged in the water.
A summer heatwave in February was partially blamed by council harbourmaster Marty Black for the "irresponsible" behaviour of swimmers, who crowded the pontoon to cool off.
Temperatures in the town have again exceeded 30degC recently, meaning the reappearance of the pontoon in the lake should be welcomed by swimmers.
