Streams and Rivers (part 4)

 Ponds and Lakes

What do a glass of water, a canoe, and a snowstorm have in common? They're three things that could connect you to a nearby lake. Lake Michigan, for example, is a source of drinking water; a place to go boating and swimming; and the source of winter snowstorms on its shores.

While water in streams and rivers is always on the move, the water in lakes and ponds is still, or standing, water. Although there is no definite rule to determine whether a body of water is called a pond or a lake, ponds are generally smaller and shallower than lakes. Sunlight usually reaches the bottom of all parts of a pond. Most lakes have parts where the water is too deep for sunlight to reach all the way to the bottom.

Ponds and lakes from when water collects in hallows and low-lying land areas. Rainfall, melting snow and ice, and runoff supply water to ponds and lakes. Others are fed by rivers or groundwater. Eventually, water may flow out of a pond or lake into a river, or evaporate from its surface.

Ponds

Compared to a tumbling mountain stream, a pond seems still and peaceful at first glance. Silvery minnows glide smoothly below the surface. A dragonfly touches the water, then whirs away. Lily pads with broad, green leaves and waxy, white blossoms float on the surface. This quiet pond is actually a thriving habitat, supporting a wide diversity of living things.

If you have ever waded in a pond, you know the muddy bottom is often covered with weeds. Because the water is shallow enough for sunlight to reach the bottom, plants grow throughout a pond. Plant-like organisms called algae also live in the pond. As plants and algae use sunlight to make food through photosynthesis, they also produce oxygen. Animals in the pond use the oxygen and food provided by plants and algae. You can see some common pond orgasm in Exploring a Pond.

Not all ponds exist year-round. For example, some ponds in the northern and western United States appear only in the spring, when runoff from spring rains and melting snow collects in low areas. The ponds dry up by midsummer as the shallow water quickly evaporates in the heat. Ponds in colder climates often freeze over during the winter.