The salmon is a familiar example of an anadromous fish; everyone has seen dramatic images of salmon struggling as they swim upstream to spawn. Most salmon return to their "home stream," the stream where they were born, to spawn, even though may have traveled thousands of miles away from it as adults. In the 1960s and 70s scientists learned that salmon recognize their home stream by smell.
- ... most scientists believe that salmon use special magnetic navigation to figure out which way to travel. When they get close to the mouth of the river that leads to the stream where they were born, they begin to smell the stream's special scents. They then "follow their noses" to their home stream. 
- It now seems to be generally accepted that salmon find their way back to their spawning grounds through their acute sense of smell. Just as each major city of the world has its own set of identifiable odors, each stream apparently has a unique set.
- The olfactory hypothesis for salmon homing, first presented by Hasler and Wisby in 1951, is based on three beliefs: (1) because of local differences in soil and vegatation of the drainage basin, each stream has a unique chemical composiion and, thus, a distinctive odor; (2) before juvenile salmon migrate to the sea they become imprinted to the distinctive odor of their home stream; (3) adult salmon use this information as a cue for homing when they migrate through the home-streaming network to the home tributary. 
- Wile, Dr. Jay L. Exploring Creation With Biology. Apologia Educational Ministries, Inc. 1998
- "... salmon are able to return to the streams where they were born after spending years swimming in the ocean." National Geographic