This looks like the spillway. If you go to google maps (unless you live there then you can go yourself) and find the Hoover Dam to find where they are taking this video from, looks like from the AZ side at the Kingman Wash Access Rd. The spills ways are for overflow, of course there's no water there now because the lake is too low. Several independent people are logging the levels of the water with live video at lake Mead on youtube.