Detectives with the La Porte County Drug Task Force responded to Michigan City Beach Saturday for the reported gathering.
"Detectives worked proactively to identify criminal activity and enforce applicable laws during the gathering," officials said.
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Police did not immediately provide any additional information about those arrested.
"Our priority is protecting the safety of our community and visitors to Michigan City," Chief Steven Forker said. "The recovery of three firearms and the arrests made during Operation Safe Shore demonstrate our commitment to addressing criminal activity and preventing potentially dangerous situations before they escalate."