Take, for example, the differences between Rapid River near Riggins and the Pahsimeroi River south of Salmon, Idaho. Both are tributaries of the Salmon River but the steelhead smolts they produce are very different. This is because the stream environments in which these fish live are quite dissimilar.  

Rapid River is less productive than the Pahsimeroi. Rapid is shallow and steep, 22.8 miles long it drops over 4,800 feet from its headwaters to its conjunction with the Little Salmon River. It tumbles down the eastern slope of the Seven Devils mountain range and is largely fed by snowmelt run-off.