A lake is any water-filled depression on land that is cut off from an inflow of ocean water. Any such body of water -from a puddle to one of the Great Lakes - can be considered a lake, although many people call smaller, shallower bodies of water pods. Bronmark and Hansson (1998) define a lake as a body of water in which wind primarily mixes the water column (see "The Lake Environment" later) and define a pond as one in which temperature changes induces mixing... This chapter continues to discuss several biotic aspects of lakes and ponds.