Millers River (frequently written as Miller's River) was a river in Middlesex County, Massachusetts. It has since mostly been obscured by landfill and "made land" (land created by filling of waterways). The small remaining estuary is a remnant of wetlands and open water that once divided Cambridge from Charlestown, Massachusetts. The exact historical course of parts the river is somewhat uncertain, and thus parts of the Charlestown-Cambridge and Somerville-Cambridge borders may have changed due to incorrect historical reconstruction.