Editors' Summary: Almost 40 years ago, in First Iowa Hydro-Electric Cooperative v. Federal Power Commission, the United States Supreme Court ruled that the Federal Power Act preempted almost all state controls on hydroelectric development. Over the last 10 years, though, court decisions and statutes have afforded the states increasing power to regulate areas concurrently under federal control. In this Article, Mr. Arnold examines First Iowa in light of these trends. He concludes that courts may read First Iowa today to open some avenues for the states to regulate the environmental effects of hydropower projects. Also, the states may be able to regulate these effects through §401 of the FWPCA and through other federal statutes.