It happened Friday evening around 6:30 p.m. along the Black Creek Trail near the Cary Parkway Bridge.
A woman who spotted the flasher described him as a white man in his 30s, between 5 feet 5 inches and 5 feet 10 inches tall. She said he was wearing a gray shirt and plaid shorts, and walking on the trail with his fly open.
People who were using the trail today told said that, while they didn't witness the flasher on Friday, they will now be on the alert.
They say you never know what someone like that might do next.
"Obviously he's crying out for attention, and, I mean, one thing always leads to another," said trail user Ashley Brewer. "That's what they always tell us."
"These days, people are on the edge sometimes and you never know what they're going to do next," said trail user Ashley Brewer. "So, we obviously want those kinds of people out of our society and away from us."
Cary police said they haven't had any other reports of flashers on the greenway system. However, if you saw something Friday night, they'd like to hear from you.