A 17-year-old has been arrested at a guest house in Weymouth after malicious tweets were sent to Olympic diver Tom Daley, Dorset Police said.
Daley and his partner Pete Waterfield finished fourth in the men's synchronised 10m platform diving on Monday, missing out on a medal.
Shortly after leaving the pool, Daley retweeted a malicious tweet he had received:
Dorset Police said they had arrested a 17-year-old man at a guest house in Weymouth in connection with the investigation.
Daley's father Rob died last year from brain cancer.
In an interview before the London Olympics began, Daley told the BBC: "Winning a medal would make all the struggles that I've had worthwhile.
"It's been my dream since a very young age to compete at an Olympics.
"I'm doing it for myself and my dad. It was both our dreams from a very young age.
"I always wanted to do it and dad was so supportive of everything.
"It would make it extra special to do it for him."
Twitter user Rileyy_69 apologised after causing a storm of fury on Twitter, saying: "@TomDaley1994 I'm sorry mate i just wanted you to win cause its the olympics I'm just annoyed we didn't win I'm sorry tom accept my apology."
But a message sent later from the Twitter account read: "i'm going to find you and i'm going to drown you in the pool you cocky tw*t your a nobody people like you make me sick."
Thousands tweeted their support for the young star, including his fellow Olympians.
The incident has also sparked debate over how people react to tweets made in poor taste.
On Monday evening, the hash tag #ThingsBetterThanRiley69 hit the top of the UK Twitter trends.