The man was fishing off the Lee Breakwater in New Plymouth on the afternoon of January 7 when he was approached by Joshua Russell and Malachai Rae, who are stepfather and stepson respectively.
Rae, 18, punched him, knocking him over, and then kicked him in the head before Russell, 39, asked him if he had tried to lure a child into his car with $3.
After Rae called the man a paedophile, both he and Russell threw his fishing rod, filleting knife and other fishing gear into the ocean.
The summary said the man was fearful and tried to empty his pockets to show the men he did not have any money.
But Russell kneed him in the face and then punched him several times.
As an attempt was made to drag the man along the jetty, he managed to get up, only to be punched by Russell again.
The force of the punch caused him to fall off the jetty and into the water, striking his ribs as he fell.
According to the summary, he tried to pull himself out of the water as he cannot swim and was fearing for his life.
But Russell held the man underwater with one hand and punched him with the other.
"At times the defendant Russell was holding the victim, by the head or throat, under the water for periods lasting 20-30 seconds," the summary stated.
Russell yelled "I’m going to kill you" to the man but released his grip on him when two bystanders intervened.
As a result of the assault, the victim was taken to hospital to be monitored for concussion and secondary drowning.
He suffered several other injuries including swelling and bruising to the face and head, his right eye was swollen shut and his front teeth were knocked out.
On Thursday, Rae and Russell appeared in New Plymouth District Court, where they pleaded guilty to the offending.
Rae admitted a charge of injuring with intent to injure and Russell, who appeared via audio-visual link from prison custody, admitted charges of injuring with intent to cause grievous bodily harm and threatening to kill.
Judge Tony Greig ordered pre-sentence reports for both men and referred the case to restorative justice.
They will be sentenced on July 23.
By Tara Shaskey