Authorities say after being groped, the woman yelled,"Stop that man he assaulted me." Another man ran after the suspect, but lost him around some nearby apartments.
Police say the same man also exposed himself to another woman as she was walking around the lake.
Apex Parks and Recreation posted crime alert signs with the suspect's description around the area Tuesday.
The suspect is described as a white man in his mid to late 20s. He has a slim build, reddish brown hair and is approximately 5'7" to 5'11". He was wearing a light blue T-shirt and blue jeans.
Nancy Burns says she believes she saw the man.
"I saw this guy and I said 'Hey' to him and he just looked at me shyly and looked down and he just kept on going he didn't bother me," Burns said.
Park user Debbie Hatt says she learned about the attack through an e-mail from a friend who was at the park at the time of the attacks. They told her, "We saw the man and noticed that he looked very odd."
"I'm shocked because I let my children ride their bikes around here," Hatt said. "I've been looking around, behind my back every minute just to be safe."
Authorities say there are also gaps on the trail where park visitors won't see anyone for a few minutes and someone could pop out of the woods and attack.
"The Parks and Recreation man told me you will see him out here, that usually when they strike once they strike again in the same place," park user Nina Gay said.
Police are working on a composite picture of the suspect. They say they hope to post it around the park Wednesday.
"I won't be walking out here by myself in the mornings which I do several days a week about that time and I won't do that anymore because that's scary," Burns said.
Anyone with information about the suspect should call Apex police at (919) 362-8661.