This paper describes and pin points the factors that led to the formation of an urban canyon in Lima, Peru. The streambed of the Rimac River deepened approximately 20 m downstream of the Army Bridge. As the river formed the canyon, several structures located downstream, such as the Dueñas Bridge, were affected. Remedial measures that locally controlled the erosion of the streambed are presented. Solutions are considered partial because it is thought that restoration of the river prior to the formation of the canyon is impractical and very costly. Recently occurred events and announcements related to new interventions in the Rimac River are also discussed. © 2011 ASCE.