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.

The singer is talking and "expected to make a full recovery", her lawyer said.
Rebecca J Thyne said she had visited Mitchell on 26 June, and the singer was "happy to be home".
The comments came in papers relating to Mitchell's conservatorship, and follow reports last month that the Big Yellow Taxi singer was unable to speak.
David Crosby - who dated Mitchell in 1967 - told The Huffington Post the star faced a long "struggle" after  being found unconscious in her home on 31 March.
"She took a terrible hit," he said. "She had an aneurysm, and nobody found her for a while. And she's going to have to struggle back from it the way you struggle back from a traumatic brain injury.
"To my knowledge, she is not speaking yet."
But Mitchell's lawyer has painted a more optimistic picture.
"When I arrived she was seated at her kitchen table feeding herself lunch," Thyne wrote.
"She also told me that she receives excellent care from caregivers round-the-clock. It was clear that she was happy to be home and that she has made remarkable progress.
"She has physical therapy each day and is expected to make a full recovery."
The court filing recommended that Mitchell's longtime friend Leslie Morris, who has been acting as her temporary conservator, be officially appointed her conservator.
According to Thyne, Mitchell should be judged to lack the capacity to give informed consent for medical treatment.

The data has been released on the internet for use by the global scientific community.
The ash tree genome map is the latest advance in fighting Chalara, which causes ash dieback.
According to new figures, ash dieback is spreading rapidly in Britain and has been found in more than 200 woods.
Evidence from continental Europe suggests that as many as 90% of ash trees could eventually die from the infection.
Scientists are searching for genetic clues to why some trees appear to be able to survive.
A team at Queen Mary University of London, has mapped the genome of a native ash tree for the first time, as part of the research.
The tree came from a wood in Gloucestershire owned by the Earth Trust.
Dr Richard Buggs of Queen Mary University of London, said it was a big leap forward.
He told the BBC: "This is the best available sequence for ash - and it is therefore a very good reference for anyone working on anything to do with ash trees."
In June, the DNA sequence of a Danish ash tree with resistance to the disease was revealed by a team at the Sainsbury Laboratory (TSL) , the John Innes Centre and the Genome Analysis Centre in Norwich.
They have also sequenced the DNA of the fungus.
An online game, Fraxinus, which the public can use to help scientists improve their data analysis, has been launched by the Norwich team.
It has been played by nearly 20,000 people from more than 100 countries.
The long-term goal is to map the genes that give a minority of ash trees resistance to the pathogen.
"The genome sequencing work is really increasing the number of genetic variants we've identified, which will help us to associate sources of variation in the tree with the genetics," said Dr Dan MacLean of TSL.
Ash dieback was first discovered in the UK in February 2012 in an import of nursery stock.
In the autumn, a small number of cases were discovered in ash trees in established woodland in Norfolk and Suffolk.
Forests in the south and east are among the worst affected, and the disease has now spread to woodland and nurseries across the UK, according to the Forestry Commission.
More details of the ash genome sequencing work and an interview with Dr Richard Buggs can be heard at 1100 BST on BBC Radio 4 on Friday, 27 September. Ashes to Ashes is presented by Professor Adam Hart and produced by Ania Lichtarowicz.
A man has been arrested on suspicion of attempted murder after a stabbing during a night of disorder in London's Hyde Park.
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Joni Mitchell has made "remarkable progress" since she suffering a stroke and brain aneurysm in March, according to court documents.
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UK scientists have mapped the genome of the British ash tree, in research to find a way to protect woodlands from a deadly fungus.