Water governance in the South Saskatchewan River Basin (SSRB), a transboundary river basin in western Canada, occurs in one of the world’s most decentralized federations. The provinces sharing the SSRB—Alberta and Saskatchewan—have primary responsibility for governing water scarcity in the basin and have done so with minimal intergovernmental coordination, oriented around an interprovincial apportionment of their shared waters, and with little involvement of the federal government. While most studies of transboundary river basin governance have focused on the importance of intergovernmental collective action, the SSRB case highlights the importance of governmental policy innovation. The decentralized nature of SSRB governance has allowed Alberta to pursue a ‘cap and trade’ policy innovation and Saskatchewan to pursue a centralized management policy innovation simultaneously, creating an unusual degree of policy divergence between two basin-sharing jurisdictions. In this way, the SSRB shows a different ‘face’ of federalism that is not as evident in most other cases, that is, the capacity for federalism to spur sub-national policy innovation in addition to intergovernmental cooperation.