“They can keep their pollution on their side of the lake.” This was the quoted response of the Chicago Park Superintendent when he was snubbed by Indiana officials who would not let him testify at a hearing involving the BP oil refinery expansion in Indiana, which would increase pollution in Lake Michigan. Of course, pollution does not stay on just one side of a lake, and many environmental decisions in one state affect other states and their citizens. Putting aside the merits of the BP expansion and permits (which are still being debated), the BP conflict shows just how poorly we manage interstate environmental harms. Current state and federal laws may even encourage interstate harms as a political externality. In an article just published by the Harvard Environmental Law Review, I propose a new state-based policy as a potential solution. States should adopt an “interstate environmental impact assessment policy” to “provide a procedural mechanism for an affected state and its citizens to influence the source state and minimize or prevent interstate environmental harms.” The citation for the article is Noah D. Hall, "Political Externalities, Federalism, and a Proposal for an Interstate Environmental Impact Assessment Policy," 32 Harvard Environmental Law Review 49 (2008). Download Hall_IEIA_article.pdf