A Hole in the Ground
 When the last ice age ended and the glaciers retreated about 12,000 years ago, they left behind millions of depressions in the ground in the north central United States and parts of Canada. The depressions are all different shapes and sizes.
 Today, these depressions fill up with water when it rains and when the snow melts. Since most of these depressions are in the prairies and they're often round like a pot, they are called prairie potholes. Some of them are temporary; others are permanent, depending on their size and amount of rainfall. |
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For the Birds
 Bulrushes, sedges, and cattails grow on the edges of prairie potholes and make great hiding and nesting places for birds and other animals. Over half of the migratory waterfowl in North America depends on prairie potholes for their survival and reproduction. Prairie potholes often absorb water that would otherwise flood inhabited areas. They also absorb sediment and nutrients that could harm rivers and streams. Prairie potholes are also sometimes called sloughs. They can be found in Montana, North and South Dakota, Iowa, Minnesota, and the Canadian prairies.
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