Ottawa Police are investigating after a man in his late teens was allegedly knocked unconscious, sexually assaulted and left naked in a downtown park.

Police say it happened in Riverain Park which is along North River Road in the Vanier neighbourhood between 6:30 p.m. and 10:30 p.m. on January 6, 2015.

Police say a man in his late teens walked along Marguerite Avenue to Washington Avenue and into the park.

Police say the man was then struck and fell unconscious.

When he came to he was naked and sexually assaulted, police said.

The man walked away from the park after finding his clothing and was taken to a safe place by a couple.

There is no description of the suspect available but investigators say the victim was wearing an orange and yellow reflective vest. Anyone with information is asked to contact police at 613-236-1222 ext. 5944 or Crime Stoppers at 613-233-8477.