While currently in several California fish hatcheries a bacteria has attacked the trout, in some areas of the Sierras, planted trout have destroyed some of the native residents.
One such example has been the demise of the Mountain Yellow Legged Frog in Kings Canyon National Park due to trout plants done there decades ago. Consequently, in the last 30 years I believe that there have been no further trout plants in Kings Canyon NP. In fact, there is an ongoing effort to rid a small percentage of the lakes of trout to give the frogs a chance to repopulate.
Two weeks ago I hiked the Old JMT (now unmaintained for nearly 80 years) through Center Basin, over Junction Pass (13,200'}, down to the Shepherd Pass Trail, over Shepherd Pass, and down Tyndall Creek. (Junction Pass still has an old sign, but was abandoned in the 1930's when the JMT was rerouted over Forester Pass.) In Center Basin at Golden Bear Lake (11,175') and the smaller lakes downstream, I observed gillnets in the water, with fresh labels made by the Park Service and a brief explanation concerning their purpose.
While I sat and enjoyed lunch and the awesome scenery at these lakes, I observed neither fish nor frogs. It will be interesting to see how things plays out. (ie, I now have an excuse to return there in a few years as a followup!)
Jim
PS- I have seen great numbers of trout up in the Meysan Lakes They were planted there a hundred years ago by Lone Pine resident Felix Meysan. To get to these Lakes, take the Meysan Lakes Trail which begins in the Whitney Portal Family Campground.