The boat is said to have been travelling at high speed, and the young people involved are between 18 and 19 years old.
"We will hold interviews during the day to clarify what happened," says Emelie Lundqvist at the police.
One person is seriously injured, she said. The Swedish Maritime Administration told TT earlier this morning that two people were involved.
One person is being treated at Sahlgrenska University Hospital and the injuries are stable.
The other five were taken to Norra Älvsborg County Hospital.
One is seriously injured, but the situation is stable, says Maria Bertilsson, an emergency officer.
An 18-year-old man is suspected of gross negligence in maritime traffic and gross drunkenness.
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