The final day of the European and British National Powerboat championships was cancelled after a man died when a boat "flipped over", Essex police said today.
A second man from the same boat suffered a head injury and was taken to hospital after the incident in Harwich, Essex, yesterday afternoon.
An Essex Police spokeswoman said it was thought the boat struck a wave before it overturned.
The spokeswoman said another boat was also affected by the wave.
Officers from the Essex Police marine unit were investigating and liaising with the Marine Accident Investigation Branch (MAIB), she added.
She said: "Around 4pm on Saturday afternoon, July 31, a powerboat appears to have flipped over.
"Two other boats stopped to help but sadly one man has died.
"The other man has been taken to hospital in Colchester by ambulance."
Police confirmed today's powerboat races will not go ahead following the incident.
A spokesman said: "The powerboat racing has been cancelled but the funfair and side shows are still taking place."
The coroner was informed of the death but no details of the dead man have been released.
Police are appealing for anyone with photographs or video of the moment the boat overturned to contact them on 0300 333444.