The demonstration was the first to turn violent since protests over water shortages kicked off on November 9.
Iran riot police have deployed in force in the Iranian city of Isfahan, a day after dozens were arrested in violent protests over the drying up of a lifeblood river.
"We have arrested 67 of the main actors and agitators behind the troubles," police General Hassan Karami said on Saturday. He said between 2,000 and 3,000 "rioters" took part in the protest on Friday.
Security forces fired tear gas during the clashes with stone-throwers in the protest in the dry bed of the Zayadneh Rood river that crosses the city, Fars and ISNA news agencies said.
On Saturday, the situation was "calm" and streets empty, with riot police deployed on the city's Khadjou bridge, a Isfahan city resident said.
The demonstration was the latest since protests kicked off on November 9 in Isfahan, some 340 kilometres (210 miles) south of Tehran, a tourist magnet due to its majestic mosques and heritage sites, including a historic bridge across the river.
But it was the first to turn violent.
Protests over dry river
During the clashes on Friday, some people set fire to objects in the city, Fars and ISNA reported.
"After the farmers left, the opportunists and counter-revolutionaries were left behind, which made it easy for the security apparatus, especially the police, to identify and arrest those who destroyed public and state property," Isfahan police chief Mohammad Reza Mirheidari said on television.
But members of the security forces were hit by fire from hunting rifles, he said, without specifying how many.
One of them was stabbed, although his condition was not believed to be critical.
According to Fars, farmers and local authorities struck a deal on Thursday about water distribution.
The riverbed has been the rallying spot for farmers and other people from across Isfahan province protesting the lack of water.
Drought is a cause, but they also accuse the authorities of diverting water from the city to supply the neighbouring province of Yazd, which is also desperately short on supplies.