Evaporation rates were measured at Lake Mead from March 2010 through February 2012 for phase 1 of an evaporation study (Moreo and Swancar, 2013). Phase 2 of the study (March 2012 through September 2017) continues evaporation measurements at Lake Mead and begins evaporation measurements at another lower Colorado River Basin reservoir, Lake Mohave. Eddy covariance is the primary measurement method. Data currently (10/6/2015) are being collected for the phase 2 study. This USGS data release represents tabular data in support of the evaporation study. The data release was produced in compliance with the new 'open data' requirements as way to make the scientific products associated with USGS research efforts and publications available to the public. The data release consists of 2 separate items: 1. Lake Mead evaporation data from March 2010 through April 2015 (Microsoft Excel workbook) 2. Lake Mohave evaporation data from May 2013 through April 2015 (Microsoft Excel workbook)