Officers responded around 12:23 p.m. to investigate a hunting-related incident on the Lewis & Clark Trail at the August A. Busch Memorial and Weldon Spring Conservation Area.
"A hunter accidentally shot a hiker, thinking he was a turkey," wrote the St. Charles County Police Department on Facebook.
Rescue crews used a utility-task vehicle to reach the injured man, who was airlifted to an area trauma center in serious condition, Kyle Gaines, a spokesman for the St. Charles County Ambulance District, told KSDK of St. Louis.
Rebecca Brown, a long-distance runner who came upon the scene Saturday, said she observed emergency responders trying to help a man on a stretcher who was nearly covered by a yellow tarp and looked unresponsive, according to the St. Louis Post-Dispatch.
Brown said another man was dressed from head to toe in camouflage nearby. She noted that he was silent and held a long firearm, the paper reported.
"It may have been an accident, but it is positively unforgivable that they allow people to hunt with firearms on Mother’s Day weekend on one of the most heavily traveled trails," argued Brown. "They need to mark that differently. There were families out there today with kids and dogs."
Nancy Phillips, of St. Louis, told KSDK she regularly hikes in the area the man was shot, and typically wears bright colors, so "no hunters mistake me for anything."
The shooting occurred on the second-to-last day of spring turkey season. The firearms season ran from April 19 to May 9, a half-hour before sunrise to 1 p.m., according to the Missouri Department of Conservation.
Authorities have yet to identify the wounded hiker and the hunter, who is reportedly cooperating with police.
The shooting is under investigation, the department said.