Police say around 12:45 p.m. Thursday, a woman and her child were sitting at a picnic table at Dingle Creek in Simcoe, Ont.
A man approached them and sat nearby. The man waved at them and then reportedly committed an indecent act.
The mother and child left the area and contacted police.
OPP describe the suspect as a white man around 50 years old. They say he was medium height with brown hair.
He was wearing brown sunglasses, a blue T-shirt with a muscle shirt underneath and jean shorts.
Anyone with further information or video surveillance is asked to contact the OPP at 1-888-310-1122 or Crime Stoppers at 1-800-222-8477 (TIPS).