This is not a dam.  Rae's Creek is dammed by a earthen embankment here to form the lake and the canal, which have equal water level.

The embankment is here.
https://www.openstreetmap.org/way/952456924

There is a spillway here.
https://www.openstreetmap.org/way/545715329

Under typical conditions the water level is regulated by letting water down the canal here.
https://www.openstreetmap.org/way/478371980