The sperm whale freed from stranding off Timaru might have been a risk-taking juvenile that simply swam too close to shore, a rescuer says.
The whale stranded off Caroline Bay on Sunday morning, and helped by a frantic day of rescue efforts managed to swim to safety at high tide.
Beaches further along the coastline were being checked this morning for any signs it might strand again.
Rescue organisation Project Jonah and the Department of Conservation used a sling around the whale attached to a fishing boat to pull it out to sea.
"A whale weighs many tonnes ... it had actually sunk into the sand" - Project Jonah general manager Daren Grover
During low tide they brought in two diggers to create a channel to help with refloating it, because it had sunk into the sand, Daren Grover from Project Jonah said.
"While we had low tide the diggers got out there, they lowered the level of the beach between the ocean and the whale and we believe that's what helped towards refloating it just after dark last night.
"As the whale was released from the suction of the sand it then became free swimming.
"The boat started to move out towards the ocean ... the whale was actually able to swim by itself out of that sling."
One of the diggers creating a channel from where the whale had sunk into the sand out towards the sea. Photo: @ProjectJonah
By mid-evening when the whale was swimming under its own power the Coastguard worked to shepherd it into deeper water.
"A whale of that size is probably a late juvenile young adult male and they're known to take risks in coming close to areas they're not normally seen in," Glover said.
"It's quite shallow there, close to shore, in Caroline Bay. It could simply have just been a bit lazy and not been watching which direction it was swimming in, and came into the shallows and got stuck."
The whale appeared to be strong and was not showing any signs of underlying physical problems or illnesses that can cause the mammals to strand.