Culverts throughout the country are approaching or are past their original design lives. These ‘baby boomer’ culverts will need to be repaired, rehabilitated, or replaced. Because entire culvert replacement is so expensive and intrusive, alternate measures to extend the culvert project life are growing increasingly popular. One such method is slip lining, where a ‘sleeve’ is installed within an existing culvert barrel and stabilized. Plastic pipe sleeves are very popular for slip lining primarily because the plastic material's lower Manning's roughness values allow for the culvert capacity to be maintained despite a reduction in culvert size. Unfortunately, the reduced friction within the barrel can create a barrier to fish passage due to increased water velocities. The increased velocities also cause greater outlet scour which can result in further obstacles to fish passage. These new fish barriers can greatly affect aquatic ecosystems by limiting the access that fish have to smaller tributaries used for spawning and rearing—access that is critical to the life cycles of many fish. It is suggested that mitigation of the increased velocities should go hand-in-hand with slip lined culvert design projects where fish passage (present or future) is to be considered. Can the demand for hydraulic capacity as well as the demand for fish passage be satisfied? Careful design and installation, coupled with post-project monitoring can result in slip lined culvert retrofits which successfully pass fish. Investigation of federal and state laws and various agency guidelines has informed the creation of a list of culvert conditions which should prompt consideration of slip lined culvert retrofit among other design alternatives. Additionally, a literature review and survey of all U.S. state Departments of Transportation as well as state Fish and Wildlife Departments has shown that there has been very limited experience in providing for fish passage through slip lined culverts. Literature and practice has pointed to the use of baffles and tailwater control weirs for velocity mitigation. Site visits have been made to the few states with this experience to assess developing technologies and record successful and unsuccessful installations. Additional hydraulic analysis using current software suggests general trends in the effects slip lined culvert retrofits on flow type, headwater, velocity as well as the effects of tailwater control weirs. Issues of sustainability, constructability and maintenance, as well as monitoring are addressed.