I've found it difficult to locate Lake Powell historical water level (elevation) data in a clean, minimal, easy-to-process format. I hope the data sets I've compiled and made available here will remedy that situation, and be of use to others.
The 25 years of historical data here was mostly (though not entirely) compiled over a long period from usbr.gov official pages, tables, and reports. It's undergone some basic sanity checks, but caveat downloador - it hasn't been vetted in line-by-line detail.
NOTE: All data sets linked here, both individually and collectively, are provided under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International (CC BY-NC-SA 4.0) license. You are free to use, adapt, and build upon this data for any non-commercial, academic, or governmental purpose. You are free to share this data, and share any derivative works based upon it, as long as these shared or derivative works (a) credit this page as the original source and (b) license them under identical terms.
For full license details, see: https://creativecommons.org/licenses/by-nc-sa/4.0/