On January 9, 2001, the U. S. Supreme Court decision in Solid Waste Agency of Northern Cook County v. U. S. Army Corps of Engineers (SWANCC) limited the scope of the Clean Water Act's jurisdiction by limiting the definition of Waters of the U.S. The Court invalidated the “Migratory Bird Rule” as the sole basis for federal regulation of non-navigable, isolated, and intrastate waters (“isolated wetlands”) under the Clean Water Act (CWA). While specifically invalidating the long-standing policy that waters used by migratory birds were included in CWA jurisdiction (termed the migratory bird rule), the decision does not make clear which of the waters and wetlands covered by 33 CFR 328(a)(3) remain under CWA jurisdiction. In January of 2003, the U.S. Environmental Protection Agency (USEPA) and the U.S. Army Corps of Engineers (Corps) published an Advanced Notice for Proposed Rulemaking on CWA Definition of Waters of the United States in the Federal Register. This document requested input from the public as a prelude to rulemaking on behalf of the federal agencies in response to SWANCC. In the absence of clear guidance that can be applied consistently throughout the country, jurisdictional determinations have been left to the individual field offices of the Corps and USEPA and vary widely. Thus, the extent of wetlands and other waters that are impacted as a result of SWANCC still cannot be determined accurately. The potential changes in jurisdiction could alter dramatically the framework for federal-state partnerships in wetlands protection and will require changes in either state or federal programs if protection of aquatic ecosystems is to be sustained at pre-SWANCC levels. The uncertainty over the extent of the change restricts the states' ability to respond. Despite this uncertainty, some states have taken action. Wisconsin passed legislation in the months following the SWANCC decision. Several other states have attempted to make changes through legislation, regulations, and/or guidance with limited success. In half of the states in the U.S., there are no state programs in place or planned to address the reduction in federal jurisdiction. In these states, a significant change in federal regulation could mean the loss of important wetlands.