How do salmon fish return to the exact spot where they were born to spawn?

salmon are born in fresh water, migrate to the ocean, then return to fresh water to reproduce. However, there are populations of several species that are restricted to fresh water through their life.
Folklore has it that the fish return to the exact spot where they were born to spawn; tracking studies have shown this to be true but the nature of how this memory works has long been debated.
The salmon spend about one to five years (depending on the species) in the open ocean where they become sexually mature. The adult salmon return primarily to their natal stream to spawn. precise method salmon use to navigate is still a mystery, though their keen sense of smell is involved.