Mead and Powell absolutely dwarf any other reservoir that are upstream. Both are below 30%.
Mead capacity at 29 million acre feet
Powell 26 million acre feet
All of the dams on the main stem (includes Powell and Mead) have a combined 58 million acre feet.
Upper basin 10 million acre feet
Lower basin 10 million acre feet.
https://en.m.wikipedia.org/wiki/List_of_dams_in_the_Colorado_River_system
Here is another list of all reservoirs upstream from LakePowell. They are at 65% capacity. 6 million acre feet.
Reservoirs Upstream of Lake Powell
They could basically empty Powell and every reservoir feeding Powell and the result would be Mead would still not being at capacity.
Tell me about that manipulation of lake levels.