Freshwater is a fleeting natural resource that can never be fully harnessed or appropriated by humans. It evaporates from the sea and land, is drawn into the atmosphere, falls as rain and snow, sinks into the earth to reappear in watercourses, and then drains back into the sea. Nonetheless, under both domestic and international law, freshwater is a regulated resource and legal principles have developed to govern its allocation and use. But what of freshwater that, rather than flowing naturally, has been made to so flow by human intervention? Should manmade canals, for instance, be subject to the same legal principles that govern the ownership and use of naturally occurring rivers? In this article, I take a first step toward clarifying when and how international water law principles applicable to natural transboundary waterways should be applied to artificial transboundary waterways. While I focus on artificial waterways in the transboundary context, I approach the issue from a domestic water law lens. I suggest that general insights may be drawn from the experience of domestic courts in solving water-related problems that exist also at the international level but that international law does not currently address. Specifically, I examine the treatment of artificial waterways in American water law as a case study. In Part 1 of the article, I discuss artificial waterways in the international context, examining international court decisions, treaties and other cross-border regimes relevant to the regulation of transboundary artificial waterways. I conclude that there is no uniform approach in international water law to the treatment of transboundary artificial waterways. In Part 2, I turn to American water law, examine the legal definition of artificial waterways, and identify two basic principles that have guided American courts in determining the legal status of such waterways: the physical attributes of the artificial waterway and whether it has legally “become” a natural watercourse. In Part 3, I suggest that these two principles could also inform the regulation of transboundary artificial waterways and the resolution of disputes arising from their use, and apply them to the Silala case currently before the ICJ. In Part 4, I offer brief conclusions.