Background and Rationale Aquatic ecosystems in urban environments are highly modified by human activity, engineering, and design. These systems are critical in delivering ecosystem services to urban residents, who comprise over 80% of the US population. This synthesis working group builds upon two impromptu meetings of interested persons held at the 2012 ASM[1]. Based upon our discussions, we propose to initiate comparative analyses of modifications of urban aquatic ecosystems in different parts of the U.S., exploring both the drivers/motivations for those modifications as well as the consequences for ecosystem function and for people, and potential feedbacks between drivers and consequences. Urban aquatic ecosystems are varied: from streams draining small, suburban watersheds to buried streams in pipes; from retention basins and ponds to bioretention cells; from natural lakes and wetlands surrounded by urban development to constructed lakes and wetlands (including wastewater treatment wetlands), among many others. Many urban areas develop along rivers or estuaries. Hydrologic modification associated with urbanization is often extensive, involving hard engineering or “soft” design. We intend to focus on these modified aquatic ecosystems to assess their prevalence, distribution, and function across several LTER sites that have an urban research focus. We ask, what are the primary drivers or motivations for urban water infrastructure design, and how do different infrastructure designs affect hydrologic connectivity, aquatic ecosystem function, and the delivery of ecosystem services? A large group participated in our initial ASM meetings, and many potential research questions and hypotheses emerged that illustrate the richness of the discussion. With available data resources as well as work already completed at several sites, we have a strong foundation for this working group’s activities.