Dam Breach: Taum Sauk Lake
Gateway Pundit has a post with other information, including some pictures and vid of an early local news. There are reports that lots of stuff has been washed away and people stranded in cars along a nearby highway, all pretty sketchy right now. No verified specifics on injuries or if people are missing or dead, either.
It's an unusual reservoir system. Built as a two reservoir system with the higher on the top of a mountain, it is designed to recycle the water between the higher and lower reservoirs. Operation is to assist with peak electricity demands. I guess ideas come in all kinds and failures are the last corrective.