The vandal who broke Wellington's Len Lye waterfront sculpture has pleaded guilty to wilful damage.

Police charged Hunter Macdonald, a 28-year-old Wellington local, after he wrecked the 'Water Whirler' sculpture in October.

Footage posted to Facebook shows him swinging on the 'Water Whirler' sculpture as it bends over the water. As he makes his way across the sculpture, it snaps and he falls in the water.

Wellington Mayor Justin Lester told RNZ the sculpture cost more than $1 million to install.

Macdonald claims he never saw a sign saying not to climb the statue and was "bored out of his mind" when he decided to swing on it.

"I decided to stop and sort of attempt some sort of gymnastic, acrobatic stuff on the sculpture," Macdonald told Stuff.

"A crowd started to form, sort of egging me on - I think they enjoyed watching it. I was sort of taking it further and further... before I knew it, the sculpture snapped so suddenly [and] came down hard on my head."

Macdonald was treated in hospital for injuries. Insurance will cover the cost of repairing the sculpture.

He will be sentenced next year, while the cost of reparation is still being sought.

Newshub.