In collaboration with Drs. Robert Hall, University of Wyoming, Colden Baxter, Idaho State University, and Ted Kennedy, Grand Canyon Monitoring and Research Center USGS (research funded by USGS), we are using quantitative food web approaches to examine the energetics and potential food limitation of the endangered humpback chub in the Grand Canyon reach of the Colorado River below Glen Canyon Dam. We are employing a large number of tools to reconstruct an extensive carbon budget and energetic food web of the river. These data will inform management of this highly altered but treasured ecosystem.