OK. The only misconception or falsehood in the claim of lemming suicide, is the use of the word suicide. According to National Geographic, lemmings DO leap into the waters en masse....but it is in search of food...not because they're fed up with life. NG believes that this fact, is the root of the myth. But the fact remains, they do leap into the waters.
From NG....
Lemming populations throughout Scandinavia tend to explode naturally every three to five years, causing huge numbers to go in search of food. Occasionally this leads the rodents to jump into water and swim to new pastures—the origin of the myth that lemmings commit mass suicide.
