Abstract:The Baltic Sea and the North American Great Lakes are two transboundary watersheds that are at risk from similar environmental stressors including nutrient enrichment, hydrologic modifications, chemicals of emerging concern, and the overarching stressor of climate change. Although located in different geographical regions of the world, both watersheds are governed in a multilevel governance setting with many layers of decision makers including global, national, governmental, regional, municipal, and community levels. Despite governance innovations, such as the Helsinki Convention in 1974 and the Great Lakes Water Quality Agreement in 1972 and their updated versions, both transboundary waters are under increasing stress from eutrophication. There are provisions in both the Helsinki Convention and the Great Lakes Water Quality Agreement for nutrient abatement measures, yet algal blooms abound in both waters, especially after precipitation events. This paper looks at the governance processes in both transboundary ecosystems, with the aim of highlighting governance barriers to eutrophication mitigation using four analytical lenses. A comparison of the two systems and the governance barriers shows that similar and unique challenges are faced in both regions, and the choice of analytical lens affects the perception of barriers and implementation actions. This is useful for policymakers in planning intervention strategies to tackle the stressor of nutrient enrichment in both regions.