In January 2009, the EPA agreed to respond to the Center for Biological Diversity’s (CBD’s) petition requesting it to modify its marine pH water quality criteria to reflect ocean acidification. Ocean acidification, however, is a by-product of increasing concentrations of carbon dioxide in the atmosphere. Thus, climate change has come to the Clean Water Act—and in May 2009, the CBD filed suit in the U.S. District Court for the District of Washington to bring this point home. The question, of course, is what the Clean Water Act can actually contribute to efforts to deal with climate change. After reviewing the Act’s basic provisions (Part I) and the various kinds of impacts that climate change is likely to have on water quality in the United States (Part II), this Article systematically evaluates the contributions that the Clean Water Act can (Part III) and cannot (Part IV) make to efforts to respond to climate change. It argues that the EPA and the states could use the Act to: (1) make valuable contributions to the nation’s efforts to gather information about actual climate change impacts on water resources and to promote more effective modeling of future impacts; (2) generate expert recommendations about potential responses to those impacts; and (3) encourage and require states and the EPA to implement water quality standards, permitting requirements, best management practices, and other measures to blunt the worst water quality impacts from climate change, increase protections for particularly sensitive areas, and increase the resilience of aquatic species, aquatic ecosystems, and the socio-ecological systems dependent upon them. However, the Article also argues that the Obama Administration and Congress could implement several changes to the Act and its regulations that would increase its effectiveness as a climate change adaptation tool. Finally, the Article concludes that even though the total maximum daily load (TMDL) provisions could be interpreted to reach greenhouse gas emissions, such an interpretation would lead to costly and ultimately ineffective efforts to make the Clean Water Act a climate change mitigation tool—a role for which the Act is not at all suited.