BackgroundHabitat that is necessary for the survival and recovery of a species listed as threatened, endangered, or extirpated (i.e., Critical Habitat) is protected in Canada. For aquatic species, Critical Habitat may include riparian habitat, however it is unclear how much of this riparian habitat needs to be protected to support the survival and recovery of a listed species (primary question). To provide quantitative evidence to support the delineation of riparian Critical Habitat, the systematic review will be used to determine the relationships between aquatic and riparian attributes and the dependence of these relationships on the quantity of riparian habitat (secondary questions). MethodsWe will search for primary research articles in bibliographic databases for primary literature, theses, and preprints and for grey literature including reports published on relevant organizational using a search string consisting of substrings for riparian habitat, and for riparian processes (i.e., erosion, filtration, infiltration, shading, and subsidization) or aquatic attributes. The results will be screened at title and abstract, and full text levels against predefined inclusion criteria and consistency checking will be performed on a subset of 100 records to ensure the inclusion criteria are consistent across multiple reviewers. Quantitative data on the riparian and aquatic habitats will be extracted and synthesized to perform dose response meta-analyses. First, the riparian habitat attributes will be combined using probabilistic principal component analysis to develop appropriate dependent variables that describe riparian habitat types. The principal component axes will then be used in a multiple regression analysis along with a measure of the riparian habitat size, and study specific identifiers and modifiers to determine the shape of the relationship and the magnitude of the effect of on the aquatic habitat. These analyses will be used to determine the extent of riparian habitat required to maintain natural levels of riparian process to protect aquatic Critical Habitat. The findings of the systematic review will support the delineation of riparian Critical Habitat for aquatic species at risk in Canada.