RIVERTON (WNE) — A 9-acre grass fire that destroyed three structures  Aug. 25 on the Wind River Indian Reservation was started by fireworks, officials said last week.

At least one of the structures was occupied, but no one was injured in the blaze, which was reported at about 5:45 p.m. Sunday on Red Crow Street south of town.

Riverton Volunteer Fire Department chief Henri DeClercq said multiple agencies responded to the incident, including the Bureau of Indian Affairs Division of Forestry and Wildland Fire Management, which sent in a helicopter to assist.

DeClercq said the helicopter was a “huge help.”

“We were actually extremely lucky we had that,” he said, adding that it was the first time he’d worked a fire with an air asset.

The BIA stations the helicopter in Fort Washakie for the summer in case of wildfires, which are more likely to spark in the hot, dry months — especially on windy days.

DeClercq said a red flag warning was in effect Sunday, when wind gusts reached 50 mph, temperatures hit 80 degrees, and there was low humidity.

He cautioned residents not to set off fireworks on red flag days, or in the late summer in general.

“With the vegetation the way it is, and with the temperatures and the winds the way they are, I see no reason to be lighting fireworks,” DeClercq said.