At least 22 people, including police personnel, were injured in the stone pelting, police said.
Farmers were protesting outside the Collectorate, seeking discharge of water from canal of Akkalpada dam to nearby villages, they said.
The injured also include farmers and Collectorate employees, added police.
Farmers had protested on April 20 with the same demand and asked the District Collector to finish the work on the last stage of the dam by September 30.