Scunthorpe's Jack Burnell was left fuming and perplexed after being disqualified from the men's open water swimming when in medal contention.
The Briton was in the Olympic medal mix at the end of the 10-kilometres race, but was denied in the frantic finale.
Initially he was in a photo finish for third, behind winner Ferry Weertman of Holland, before being demoted to fifth and then disqualified altogether for a second caution from race officials.
The 23-year-old, who was fifth in last year's World Championships, said: "It was an absolute joke, the whole thing from start to finish.
"You've got the best guys in the world out here, who have trained for four years, put a lot of hard work into this.
"This is the pinnacle of our sport and it's ruined by a couple of judges, who want to stick their nose in, just because they want something to do."