Lake mead is dropping because when they set up the selling of the water from lake mead, the data they used to determine expected future inflows were from a very wet period, so in average years they sell more water than comes into the lake, and only break even when it is very wet. They have promised x amount of water to cities and farms, and somehow can't get away from it.
Speaking of fake lakes, look at lake Las Vegas. They pump water from mead, which runs into the lake, out through the dam, and back into mead. No joke, a completely fake lake, very Las Vegas.