Michael Bartlomiej Dorynek had been out fishing with three passengers at a busy St Brelade’s Bay in July 2017 on his boat, called Severe Attitude.
At the beach, the 38-year-old invited another friend and four children on board to take them for a ride and was ‘zig-zagging’ through the water.
Meanwhile, Tyson Flath was riding his jet ski with his friend Giles Corbin as passenger.
The Royal Court heard that Mr Flath heard screaming from his left and ‘to my horror we saw a white vessel approaching us very rapidly’.
Mr Corbin was flung from the jet ski and suffered severe leg injuries.
Dorynek, who has no previous convictions, admitted one count of operating a ship in territorial waters without due care and attention – the maximum sentence for which is a £10,000 fine.
