Worsnop arranged a competition comprising various activities including a ski biscuit relay.
The relay involved each competing boat towing a person on a ski biscuit on a 600m course. They had to turn around two 5-knot warning buoys.
Worsnop and Sargeson each skippered a boat. Mr Wroe was on a ski biscuit being towed by Sargeson's boat.
Worsnop left the shore first but was overtaken by Sargeson. Worsnop attempted to turn around them in the opposite direction to the lead boat.
Having started his turn in an anti-clockwise direction, Worsnop realised that to continue would almost certainly cause a collision between his and the other boat, so he closed the throttle and the boat came to a stop.
Sargeson was already committed to the turn when he realised the other boat was heading around the buoys towards him and he also stopped.
The act of slowing while in the turn caused a pendulum effect for the biscuit behind the boat. It caused the biscuit to swing in an arc and it collided with the other stationary boat.
Worsnop realised what was going to happen and attempted to reverse but the ski biscuit struck the bow.
The impact burst the ski biscuit and flung both riders into the water.
Mr Wroe suffered serious trauma to the abdomen as well as numerous fractured ribs and ruptured spleen - injuries, police say, were instantly fatal.
The other person who had been on the ski biscuit was knocked unconscious and bruised.
The area where the incident occurred was subject to a bylaw restricting speeds to 5 knots (9km/h) within 30m of the shore, any structure including buoys and any vessel or person in the water.
Two boats involved in the race were not using spotters to watch the biscuits - a requirement of the Maritime Transport Act 1994. Sargeson had a spotter on his boat.
"He admitted that the afternoon of activities that he had organised was supposed to be a fun way for the different camps to socialise, and he was devastated that what had occurred resulted in his best friend losing his life," police said.
Sargeson was extremely remorseful and told police he assumed the two boats behind him would complete a clockwise turn so he began to complete a clockwise turn.
He said he exceeded the 5 knots partway around the turn and saw Worsnop completing an anti-clockwise turn in very close proximity to his boat.
He immediately took action in an attempt to avoid a collision but was unsuccessful.
Worsnop's lawyer Simon Lance asked a conviction not be entered at this stage. Sargeson's lawyer Murray McKechnie said it would be helpful if the men took part in the restorative justice scheme.
Judge Phillip Cooper said he would not enter convictions at this stage and remanded Sargeson and Worsnop at large for sentencing on September 7. The pair have also been referred to Mana Social Services to take part in the restorative justice scheme.
