I used to fish the alpine lakes in Washington, they do get fished, and in general need to be stocked every 3 - 5 years depending on fishing pressure. Some great fishing can be had, but there are times when you make that 5 mile hike and find the lake you want to fish has been fished out. In some of the lakes the trout reproduce, and can do well on their own, usually they have a feeder stream to spawn in, others where they can't spawn, get stocked.
Recently, they've stopped stocking the lakes in the national parks in Washington, as in their natural state, they did not contain trout. The trout can prey on native salamanders, and frogs and what not, so no more trout stocked in those lakes.
The state did some airplane stocking, but in recent years they've made back pack portable plastic bags that are filled with water and air, and can hold 500 fingerlings. Volunteers carry them in to the lakes that are still stocked and release them.