Each fall the highly endangered European Lake trout embarks on a strenuous journey from the deep Swiss Alpine lakes to return to their birthplace. Driven by a strong homing instinct the female trout migrate into small Alpine streams, where a complex spawning ritual starts. Large males follow them in high hopes to fertilize their eggs, yet the female is picky and able to choose only the best suiters for her future young. A very large male showing a behavior never before documented gets the chance to mate with the female in this harsh un-disturbed Alpine environment.