Lake Waihola. Photo by Gregor Richardson.
The boy, who was wearing a wetsuit and lifejacket, was playing with the toy in water near the playground, when a strong gust drove him across the lake, about 2pm.
Onlookers on shore watched in horror as the inflatable was blown the lake.
He was later found, clutching on to reeds on the other side of the lake - a distance of 1km.
Clutha-Taieri area response manager Senior Sergeant Alastair Dickie said the mother was distraught when police arrived.
''The wee boy was also in a bit of shock . . . he had the wind up him, so to speak.''
An ambulance was called as a precaution, he said.
''We had a wee chat and I told him ''well done son for holding on to your ... toy.''
