Three people were stabbed when thousands gathered for a water fight in the park which descended into violence last week.
The 18-year-old man was arrested earlier and remains in custody.
Another man, 18, and a 17-year-old boy, have also been arrested in relation to disorder in McDonald's in Marble Arch.
Eleven people have now been arrested after the events on Tuesday 19 July.
The arrests came after police released a gallery of photos of suspects linked to the disorder that saw three people, including a police officer, stabbed.
A second officer suffered injuries from a flying bottle as officers tried to contain aggressive crowds that had gathered.
A man has been arrested on suspicion of attempted murder after a stabbing during a night of disorder in London's Hyde Park.