How Do Fish Get Into Isolated Mountain Lakes?

Mammals walk, birds fly, and fish swim. But fish are restricted to living where there's water to live in. How did fish ever get to lake high up on mountainsides? Lake Titicaca is 12,507 feet above sea level, and it has fish. The water comes from glacial runoff and rain, but where did the fish come from? Even small mountain lakes have fish, and there have even been cases of fish living in lakes that dry up every year.

MinuteEarth gives us three possible scenarios in which fish from far away can end up living in isolated lakes, and the most likely scenario for a random mountain lake is also the most bizarre. I guess life finds a way. This video is only 2:40; the rest is an ad.