"Overwhelmingly, best practice guidance advocates the removal of weirs as the priority option for longitudinal connectivity improvement schemes. This approach not only directly and immediately addresses longitudinal river fragmentation, but also provides the best conditions for sustainable self-recovery. When done in combination with the removal of embankments and hard bank protection, and bed-reprofiling such that lateral connectivity is also improved, the river and floodplain are rightly and necessarily treated as functionally linked ecosystems.
Best practice goes on to advocate, where complete barrier removal isn’t feasible, the alternative option should be reducing the height of weirs and/or providing bypass routes. The now withdrawn Environment Agency Fish Pass Manual provides greater granularity of options at this point by advocating consideration of modification to any existing fish pass, construction of low-cost informal solutions to assist fish passage, and then finally when none of the above are applicable, construction of formal fish passes or easements.