Evretou is unsual in that it's overflow is in a different location to the actual dam. Apparently, this is down to Earthquake damage in previous years. The dam became unsafe so they built an overflow away from it at a lower level, or so I have been told.
To get to the overflow is a bit of an adventure, though I am happy to say they have made the road towards it a bit more robust in the last year. Be warned though, that when you get there, it is very muddy indeed.