WINONA, Minn. - At least 35 people have been arrested in Winona during a protest of frack sand mining.

Protesters gathered at an intersection Monday and then walked to the commercial harbor and a sand processing plant on Winona's west end.

Winona Police Chief Paul Bostrack tells the Winona Daily News that about 19 people were arrested at the city's commercial dock and another 16 at the sand processing plant after being warned they were trespassing on private property.

Winona Catholic Workers organized the protest. Protesters say their goal was to halt business operations at each site.

Dan Nisbit, owner of CD Corp., which leases the commercial dock, says the protest created a distraction for workers and temporarily slowed operations at the facility.

Frack sand is used by oil and gas drilling companies. Opponents of frack sand mining have raised environmental concerns.