Do I have to know how to swim in order to participate?

Yes.  You can skip the obstacles tha may include swim depth water so technically you don't HAVE to know how to swim is necessary to know how to swim if you want to do all of the obstacles on some courses. There might be areas on the course that require you to swim but there will also be alternate routes, guide ropes and lifeguards in those areas.  Use your head.  If you are not a swimmer and there is water over your head.....GO AROUND. There are alternate routes for those who do not want to swim.