It can occur quite frequently to see little blue flames floating over the still dark waters in the fens during nighttime.
These little glimmers are called will-o'-the-wisps and legends have it, that they are little maleficient spirits who hypnotize careless travellers to lure them into a cold death in deep black water.
So, if ever you see a will-o'-the-wisp, dont look straight at it if you don't want to drown!