Tunneling under Lake Mead

Las Vegas is digging a 1,500 foot long tunnel, 600 feet below ground through bedrock to suck water from Lake Mead, in case the lake level drops too low for the existing intake to draw water. "Intake No. 3 will maintain SNWA's ability to draw upon Colorado River water at lake elevations as low as 1,000 feet above sea level, assuring system capacity if lake levels fell low enough to put Intake No. 1 out of service." [right, Intake 3 tunnel. Credit, SNWA]

The starter tunnel is complete, ready for the boring machine to be lowered into it for assembly. An earlier starter tunnel was abandoned after it hit a fault zone and unstable rock.
SNWA has a short video explaining the project.