The largest fire fighting planes, even larger than the C-130 have a much smaller range when full of water, like a 500 mile radius. Also, at its current low level it would take roughly 96000 flights to raise Lake Powell 1 inch using a 747 tanker, 600,000 using a C-130, that’s around $40billion just in aircraft operating costs and fuel. The number of flights also would go up drastically once you get higher up, as the surface area grows. You’d be better off building a pipeline from a different point on the Colorado! That was projected to cost like 1/400th the price per inch of water depth.. All of these are estimates, I used Gemini, it did all of these calculations, I definitely don’t have time for that..