Over the past year, social networking websites such as Facebook have been used to organise the fights, which can attract hundreds of people.
Police pointed out that although the fights might seem harmless, people can get hurt and some park users might feel intimidated.
Simon Ovens, superintendent for Westminster South and Commander Royal Parks, said: 'We're now monitoring the internet and using officers to ensure this doesn't get out of hand." He declined to explain how the monitoring was done in case organisers should look for ways to evade detection.
Ovens added that when his officers learned about a planned fight, they would contact the organisers and ask whether they had permission for it and warn them of the need for third-party insurance.
If the event were not cancelled, the police would stop the fight. "Officers will confiscate water pistols and syringes of water," said Ovens.