Looks like Lake Mead follows the same rules as national parks. Concealed is okay with a valid permit for the state in question, open carry is a no go.
Thread: LAKE MEAD RECREATION AREA
I believe the law was changed allowing the carry of handguns in National Parks, the question is the Lake Mead National Recreation Area subject to this new law?
Thanks Jessel: I searched all available sites but could not find the info specfic to Lake Mead/Lake Mohave.
Lake Mohave still has the old sign up that prohibits firearms.