Figure 5.5.50 – Solutions to adapt existing drainage structures to enhance opportunities for fish passage – not recommended for any new infrastructure where best options are wider structures which allow the restoration of the stream and natural embankments at each site. A: Installing weirs stabilises the reconstituted substrate but also concentrates low flows and provides resting areas for fish. Lateral dry passages also allow terrestrial mammals to use this passage (Source: Cerema, 2021); B: Installation of weirs in a passage that is only suitable for fish (Source: Cerema, 2021); C: Stones fixed into the substrate achieve the same objective as weirs but are not suitable for mammal crossing (Source: Sétra, 2013).