Salmon and sea trout return to breed in the rivers where they hatched but they have to bypass the dam first. Parliament also required hydro-electric schemes in the Highlands to safeguard fish stocks. So engineers designed Pitlochry’s famous fish ladder, with its thirty-four tiered pools that safely shepherd them upriver and homeward. Screens keep large fish away from the turbines so that young fish can pass safely through the turbines on their return to the sea. The fish-friendly design of the blades acts like a revolving door and Pitlochry’s salmon ladder has been crossed by over 250,000 salmon since it was built in 1952.