The level of Lake Mead is controlled by the Hoover Dam. Shut off or reduce the outflow until the lake fills up again. What’s the problem? Why let the water go to waste by flowing into the Gulf of California?
Virtually none of the water makes it to the Gulf of Califonia, in spite of a treaty between the two countries.
I don’t believe any water, but a trickle, reached the Gulf of California. With several States and Mexico drawing their ever increasing water allocations from the Colorado River, the water is just about ‘spoken for’.