Images from the park show groups of young people carrying colourful water guns and having fun soaking each other in the 40C heat, according to Radio Free Europe.
But when images of the event were posted online they upset the nation’s conservatives. One conservative MP said the event was shameful and could spread “corruption”.
Shortly later, the city’s police chief Hossein Sajedina said some of those involved had been arrested.
He said participants of the water fight had been acting “abnormally” and were disobeying Islamic principles.
Those wacky Iranians, eh..?