It seems that the above photograph is taken by Ethan Miller. When I received these photos in an email forward, the above photograph's attributes/properties had his name.
Note: I received the above photos of Hoover Dam Bypass in an email forward. These are not photographed by me. The copyright and credit of these photos remain with the original photographers. If you are one of the original photographers of these images of Hoover Dam Bypass, please let me know; I'll very happily link back to you :)