Some of the most memorable scenes in White Wilderness, Disney's 1958 Academy Award-winning "True-Life Adventure" nature documentary about wildlife in the snowy northern portions of the North American continent, were ones featuring lemming suicide: the death of lemmings who drowned after jumping off cliffs and into the sea. But the scenes shown in the documentary were staged by filmmakers in order to replicate supposed real-life behavior of lemmings that could not be captured on film, and thus did Disney perpetuate for generations to come the legend of periodic, inexplicable mass suicides by lemmings who die by hurling themselves off of cliffs.

https://www.snopes.com/fact-check/white-wilderness-lemming-suicide/