Almost 97 percent of land use in the United States is non-urban, and rural stormwater management practices significantly impact the nation’s water resources. Highway departments play a major role in directing this runoff and operate within clearly established political boundaries. However, trans-jurisdictional water management is necessary because watershed and political boundaries rarely overlap. Yet, highway departments are traditionally absent from water management conversations. This dissertation conducted two original surveys at two spatial scales to investigate and explain the complexity of transboundary highway stormwater and roadside ditch management practices through the lens of integrated water resources management (IWRM) principles.The first chapter summarizes a regional-scale comparative study of stormwater management by highway departments of the six states located in the Chesapeake Bay Watershed. The study revealed states do not coordinate stormwater management strategies either through a vertical hierarchical governance framework or horizontally through cross-border coordination. No coordinated systems were in place for highway departments to integrate runoff management into broader watershed health objectives. The second chapter examines local-scale collaboration and drainage management by town highway departments in New York State. Transboundary collaboration between towns was very limited, with almost 60 percent of towns collaborating with zero or only one town. For the more collaborative towns, their “bottom-up” approach to trans-jurisdictional stormwater management was strongly correlated to time in position, good personal relationships, and sharing equipment. The third chapter builds upon an unexpected discovery that a town’s engagement with a watershed organization positively correlated with highway department collaboration and access to additional resources. A comparison of different watershed group structures suggests that citizen-operated watershed organizations have a stronger influence on highway department activity as compared to regional or government affiliated watershed groups. Across both scales, highway departments struggled with insufficient manpower, funding, and equipment, and none had a clear mandate or support to holistically manage stormwater. Combined, these chapters provide clear evidence, with new insights, to substantiate the “municipality-basin gap” theory in water governance recently proposed as a key weakness in IWRM. These findings establish a compelling rationale for including highway departments as key stakeholders in water management and watershed planning efforts.