Salmon utilise a number of habitats during their life in Scottish rivers. For spawning they require clean gravel beds that allow sufficient water to flow through the gravel and keep the incubating eggs supplied with oxygen. The fry and parr feed over cobbly river beds and shelter behind boulders and submerged debris when resting and to hide from predators.
When the parr begin to smolt and migrate downstream it is essential that there are no barriers preventing them from reaching the sea. The same is also true for adult salmon ascending the river to spawn. Dams and weirs can represent considerable obstacles to migration so many are fitted with fish passes, allowing salmon to pass the barrier by breaking the height difference into a series of manageable steps. At some sites, such as Faskally Dam in Pitlochry, facilities are provided for watching salmon ascending the ladder.
During the upstream migration, adult salmon require deeper pools for shelter and rest. They will also wait in pools for the correct time of year to begin spawning once they are close to their spawning grounds. Pools used by adult salmon can become well known locally as good fishing beats and often have a long history with strange and evocative names such as Carry Wiel, Galoshan and Weetles on the River Tweed.