Salmon are initially born in freshwater and then migrate to saltwater later on. Once salmon are ready to spawn/reproduce they go back to freshwater to do so. They begin their lives in freshwater streams and after they have migrated to the ocean and matured it is time for them to come back to freshwater in order to spawn and then eventually die.

So this particular type of fish can be found in both saltwater and freshwater, though they do spend most of their time in saltwater, at least until they have completely matured and ready to reproduce upstream again in freshwater.