For the National Hydropower Association, Brattle experts conducted an analysis of the EPA’s proposed rule for regulating CO2 from existing sources under Section 111(d) of the Clean Air Act, focusing on potential economic impact to hydropower. We summarized key aspects of the rule, and assessed how the compliance options for states could differ from the Best System of Emission Reduction (BSER) options in setting the target rates, and how states can utilize hydropower (existing or new) as a compliance option under the rule.