Salmon
As the salmon go upstream to the spawning grounds, they may face obstruction from beaver dams. Sluice gates have to be provided so the gravid female salmon can get to the spawning grounds. This is a problem caused by the re-introduction of beavers to the U.K. Sluice gates are opened for the salmon at breeding time. Salmon farms are also possible, in which the fish are non-migratory, but then they have to be fed artificially.