By this time an older girl, who had been with the boys before they got into difficulty, had called emergency services and police were on their way.
The skipper of a private jetboat which was travelling downstream was alerted to the boy's dire situation, unloaded all but one of his passengers and went to help.
Skipper Jonathon Sutherland and fellow rescuer Christopher Campbell nudged their boat well into the trees and one of the men got into the water and freed the 12-year-old's foot.
All four boys were scooped up and taken to the riverbank where the crowd had gathered and police, fire fighters and paramedics were waiting.
Paramedics declared the 12-year-old possibly had a leg injury and had swallowed water.
The 13-year-old who was caught in the current earlier was upset and cold.
Both were taken by Westpac helicopter to Christchurch Hospital, where they were met by their families.
The boy who was trapped was released from hospital the next day with only a sore ankle.
"This was a serious situation where, if it was not for the quick actions of the two men and their ability to extract the boys using a boat, the 12-year-old boy would certainly have drowned," Constable Guy Atkinson of Methven said.
"They pulled off a successful rescue during a tense situation. The pair should be extremely proud of themselves for saving the boy's life.
"It's not a day the men or the boys are likely to forget."