I've never measured it but I'm told that it is 14 miles around White Rock Lake in Dallas. What I have determined is helmets and knee pads are a must for the ride around the lake. Walking around the lake I have two often bicycle riders end up on the concrete pavement trying to negotiate the turns. This seems particularly so when they go over the brides.
Once more it supports my ideas that Mountain Bicycle (MTB) should only be ridden in the Mountains. I have never seen a Beach Cruiser end up on the pavement because these riders are typically going slower and enjoying the ride rather than racing around.
http://justbicycles.com/