Hooooo boy, do I have some books for you that I've found helpful in my research.
Slickrock by Edward Abbey
The Colorado Plateau by Donald Baars (geology)
Rainbow Bridge by Charles Bernheimer (exploration in the 1920s, focused on RB)
the University of Utah Anthropological Papers, Glen Canyon Series (anthropology and history from before the lake, generally pretty difficult to find)
Powell of the Colorado by William Culp Darrah
The Romance of the Colorado River by Frederick S. Dellenbaugh (history, by a member of Powell's second expedition)
The Glen Canyon Country by Don Fowler (general history of the area, by an anthropologist who got his start excavating Anasazi sites in Glen Canyon)
Downriver by Heather Hansman (not necessarily about Lake Powell but covers many of the relevant water issues)
Cass Hite by James Knipmeyer
The Life and Times of Denis Julien by Knipmeyer (both biographies of canyon country residents)
The Powell Expedition by Don Lago (only useful for those who want to get into the weeds of John Wesley Powell like I have)
The Ghosts of Dandy Crossing by Katie Lee (semi-autobiographical novel about the people who loved Glen Canyon and the river)
Exploring Desert Stone by Steven Madsen (history of the 1859 Macomb expedition that paved the way for John Wesley Powell)
Navajo Mountain and Rainbow Bridge Religion by Karl Luckert (Navajo beliefs and religious ceremonies about RB)
From Powell to Power by Otis 'Dock' Marston (history of the first 100 people to go through the Grand Canyon)
King of the Colorado by Tom McCourt (historical novel about Cass Hite)
Lake Powell by Loren Potter and Charles Drake (science and natural history)
Dead Pool by James Lawrence Powell (history and climatology)
Cadillac Desert by Marc Reisner (history of Reclamation)
Colorado River Controversies by Robert Brewster Stanton (John Wesley Powell's dirty laundry)
Glen Canyon and the San Juan Country by Gary Topping (general history)
The Dominguez-Escalante Journal edited by Ted Warner and translated by Angelico Chavez
The Colorado by Frank Waters (beautifully written about the whole river)
A River Running West by Donald Worster (the longest and most recent John Wesley Powell biography)
Rivers of Empire by Donald Worster (history of Reclamation, disclaimer: not recommended for light reading)
These are the books I've read that I figured people on this forum would be interested in. I have more but they're less relevant to Lake Powell itself. And then of course, there's mine but we'll all have to wait a little while for that.