Sharing the world’s largest freshwater lake system, Canada and United States seek for over a hundred years to jointly manage this vital resource. However, in accordance with multi-level governance and paradiplomacy literature, it appears that this collaboration has considerably changed over the last thirty years. From an initial bilateral cooperation between federal authorities, provinces and US states became prominent actors in cross-border water governance, and, in this sense, a green transboundary paradiplomacy has emerged along the 49th parallel. In particular, a specific cross-border organization, the Council of Great Lakes Governors, developed an interesting water regime, and adopted recently a dual tool for water governance in 2005, called the “Great Lakes – St. Lawrence River Basin Water Resources Compact” and its non-binding twin the “Great Lakes – St. Lawrence River Basin Sustainable Resources Agreement”, which aim to prevent massive water transfer outside the basin. Adopting a multi-level governance perspective, this paper aims to analyze in depth this new environmental regime and, in corollary, the effectiveness of the implementation process of this dual agreement. Then, we will begin a broader reflection on cross-border and subnational environmental multilevel governance in North America.