Waterwolf

Waterwolf, or Water-wolf is a Dutch word for the tendency of lakes in low-lying peaty land to enlarge by flooding and eroding their shores, aided sometimes by men digging peat for fuel.

The growth of any lake was seen as a direct threat to nearby villages, though the economic necessity of digging for peat by the townspeople of such villages was itself often a contributing factor. The "water wolf" could "devour the land" in times of spring tide flooding or heavy storms. See Flood control in the Netherlands, with the most notable "waterwolves" conquered being the Haarlem Lake and the Braakman.

...
Wikipedia