As relicensing and maintenance costs of hydropower generation increase, many operators are considering whether to relicense or to surrender their operating licenses. These economic decisions are made in the context of a power system that is installing historic new capacity to meet rising demand while attempting to meet company, state, and federal emissions goals and targets. This research investigates the U.S. CO2 emissions implications of retiring existing hydro generators instead of relicensing them, and the cost implications of retiring such generators under a clean electricity standard.