The degradation of inland aquatic habitats caused by decades of human activities has led to worldwide efforts to rehabilitate freshwater habitats for fisheries and aquatic resources. We reviewed published evaluations of stream rehabilitation techniques from throughout the world, including studies on road improvement, riparian rehabilitation, floodplain connectivity and rehabilitation, instream habitat improvement, nutrient addition, and other, less‐common techniques. We summarize current knowledge about the effectiveness of these techniques for improving physical habitat and water quality and increasing fish and biotic production. Despite locating 345 studies on effectiveness of stream rehabilitation, firm conclusions about many specific techniques were difficult to make because of the limited information provided on physical habitat, water quality, and biota and because of the short duration and limited scope of most published evaluations. Reconnection of isolated habitats, floodplain rehabilitation, and instream habitat improvement have, however, proven effective for improving habitat and increasing local fish abundance under many circumstances. Techniques such as riparian rehabilitation, road improvements (sediment reduction), dam removal, and restoration of natural flood regimes have shown promise for restoring natural processes that create and maintain habitats, but no long‐term studies documenting their success have yet been published. Our review demonstrates that the failure of many rehabilitation projects to achieve objectives is attributable to inadequate assessment of historic conditions and factors limiting biotic production; poor understanding of watershed‐scale processes that influence localized projects; and monitoring at inappropriate spatial and temporal scales. We suggest an interim approach to sequencing rehabilitation projects that partially addresses these needs through protecting high‐quality habitats and restoring connectivity and watershed processes before implementing instream habitat improvement projects.

Despite decades of research on wood in rivers, the addition of wood as a river restoration technique remains controversial. We reviewed the literature on natural and placed wood to shed light on areas of continued debate. Research on river ecology demonstrates that large woody debris has always been a natural part of most rivers systems. Although a few studies have reported high structural failure rates (>50%) of placed instream wood structures, most studies have shown relatively low failure rates (<20%) and that placed wood remains stable for several years, though long-term evaluations of placed wood are rare. The vast majority of studies on wood placement have reported improvements in physical habitat (e.g., increased pool frequency, cover, habitat diversity). Studies that have not reported improvements in physical habitat often found that watershed processes (e.g., sediment, hydrology, water quality) had not been addressed. Finally, most evaluations of fish response to wood placement have shown positive responses for salmonids, though few studies have looked at long-term watershed-scale responses or studied a wide range of species.Résumé : Malgré des décennies de recherche sur le bois dans les rivières, l'ajout de bois comme technique de restauration demeure controversé. Nous avons passé en revue la documentation sur le bois naturel et mis en place pour faire la lumière sur les enjeux qui font toujours l'objet de débat. La recherche en écologie fluviale démontre que les grands débris ligneux ont toujours constitué une composante naturelle de la plupart des réseaux fluviaux. Si quelques études ont signalé des taux élevés de défaillance structurale (>50 %) des structures en bois mises en place dans des cours d'eau, la plupart des études ont noté des taux de défaillance assez faibles (<20 %) et montré que le bois mis en place dans les cours d'eau demeurait stable pendant plusieurs années, les évaluations à long terme du bois mis en place étant toutefois rares. La grande majorité des études sur la mise en place de bois font état d'améliorations de l'habitat physique (p. ex. fréquences accrues de mouilles, couvert, diversité des habitats). Bon nombre des études n'ayant pas constaté d'amélioration de l'habitat physique notaient que les processus hydrographiques (p. ex. sédiments, hydrologie, qualité de l'eau) n'avaient pas été pris en considération. Enfin, si la plupart des évaluations de la réaction des poissons à la mise en place de bois ont relevé des réactions positives en ce qui concerne les salmonidés, peu d'études ont examiné les réactions à long terme à l'échelle du bassin versant ou étudié un grand éventail d'espèces. [Traduit par la Rédaction]

The placement of boulder weirs is a popular method to improve fish habitat, though little is known about the effectiveness of these structures at increasing fish and biota abundance. We examined the effectiveness of boulder weir placement by comparing physical habitat, chemical and biotic metrics in 13 paired treatment (boulder weir placement) and control reaches in seven southwest Oregon watersheds in the summer of 2002 and 2003. Pool area, the number of boulders, total large woody debris (LWD) and LWD forming pools were all significantly higher in treatment than control reaches (p < 0.05). No differences in water chemistry (total N, total P, dissolved organic carbon) or macroinvertebrate metrics (richness, total abundance, benthic index of biotic integrity etc.) were detected. Abundance of juvenile coho salmon (Oncorhynchuskisutch) and trout (O. mykiss and O. clarki) were higher in treatment than control reaches (p < 0.05), while dace (Rhinichthys spp.; p < 0.09) were more abundant in control reaches and no significant difference was detected for young-of-year trout (p > 0.20). Both coho salmon and trout response to boulder weir placement were positively correlated with difference in pool area; p < 0.10), while dace and young-of-year trout response to boulder weir placement were negatively correlated with difference in LWD (p < 0.05). The placement of boulder weirs appears to be an effective technique for increasing local abundance of species that prefer pools (juvenile coho and trout >100 mm). Based on our results and previous studies on bedrock and incised channels, we suggest that the placement of boulder structures is a useful first step in attempting to restore these types of stream channels.