A man, 39, has been arrested for allegedly assaulting another man in New Plymouth on Sunday.
The incident occurred at the Lee Breakwater around 4.30pm.
The alleged victim was approached by another man who threw him off the jetty and held him under the water, police said.
The victim suffered injuries which led to him being admitted to hospital.
Police say the man handed himself in after they called on the public for information about the assault.
He has been charged with wounding with intent to cause grievous bodily harm, and threatening to kill/ do grievous bodily harm.
He is due to appear in the New Plymouth District Court today.